PLoS Med plos plosmed PLOS Medicine 1549-1277 1549-1676 Public Library of Science San Francisco, CA USA 10.1371/journal.pmed.1003641 PMEDICINE-D-20-06245 Research Article Medicine and health sciencesUrologyGenitourinary infectionsHuman papillomavirus infection Medicine and health sciencesMedical conditionsInfectious diseasesSexually transmitted diseasesHuman papillomavirus infection Medicine and health sciencesMedical conditionsInfectious diseasesViral diseasesHuman papillomavirus infection Medicine and health sciencesWomen's healthMaternal healthBirthLabor and delivery Medicine and health sciencesWomen's healthObstetrics and gynecologyBirthLabor and delivery Medicine and health sciencesEpidemiologyMedical risk factorsCancer risk factors Medicine and health sciencesOncologyCancer risk factors Biology and life sciencesCell biologyCytology Medicine and health sciencesEpidemiologyMedical risk factors Medicine and health sciencesWomen's healthObstetrics and gynecology People and placesGeographical locationsEuropeEuropean UnionSweden Medicine and health sciencesWomen's healthMaternal healthPregnancyChorioamnionitis Medicine and health sciencesWomen's healthObstetrics and gynecologyPregnancyChorioamnionitis Associations of treated and untreated human papillomavirus infection with preterm delivery and neonatal mortality: A Swedish population-based study Treated and untreated HPV infection and preterm delivery and neonatal mortality https://orcid.org/0000-0002-9441-2035 Wiik Johanna Conceptualization Data curation Formal analysis Funding acquisition Project administration Writing – original draft Writing – review & editing 1 2 3 * https://orcid.org/0000-0003-4748-0446 Nilsson Staffan Data curation Formal analysis Methodology Supervision Writing – review & editing 4 5 https://orcid.org/0000-0002-6286-1733 Kärrberg Cecilia Conceptualization Methodology Writing – review & editing 1 3 6 https://orcid.org/0000-0001-8369-7955 Strander Björn Conceptualization Data curation Methodology Writing – review & editing 1 6 https://orcid.org/0000-0001-5079-2374 Jacobsson Bo Conceptualization Methodology Writing – review & editing 1 3 7 https://orcid.org/0000-0002-3608-7430 Sengpiel Verena Conceptualization Data curation Funding acquisition Methodology Project administration Supervision Writing – original draft Writing – review & editing 1 3 Department of Obstetrics and Gynaecology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Department of Gynaecology and Obstetrics, Østfold Hospital Trust, Kalnes, Norway Department of Obstetrics and Gynaecology, Sahlgrenska University Hospital, Gothenburg, Sweden Department of Mathematical Sciences, Chalmers University of Technology, Gothenburg, Sweden Department of Laboratory Medicine, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Regional Cancer Centre West, Region Västra Götaland, Gothenburg, Sweden Department of Genetics and Bioinformatics, Division of Health Data and Digitalisation, Norwegian Institute of Public Health, Oslo, Norway Myers Jenny E. Academic Editor University of Manchester, UNITED KINGDOM

I have read the journal´s policy and the authors of this manuscript have the following competing interests: CK has research grants for clinical trial Assar Gabrielsson’s Foundation for Cancer-Related Clinical Research, Hjalmar Svensson’s Research Foundation. She is presently head of one Swedish site of a multicenter international academic clinical HPV-vaccine trial where the sponsor, Imperial College, London, receive some support from MSD. She is a member of the Screening and colposcopy national guidelines committee, and she is the secretary of The Swedish Society for Colposcopy and Cervical Cancer Prevention/C-ARG. She has received reimbursement from Gedeon Richter for lectures on meeting arranged by the company. BS has research grants for clinical trial by the Governmental agreement with Swedish counties, ALF, and by the Region of Västra Götaland. He is presently Swedish head of an multicenter international academic clinical HPV-vaccine trial where the sponsor, Imperial College, London, receive some support from MSD. The past five years he has served as chairman of the Swedish Cervical screening coordinating committee, as chairman of the Screening and colposcopy national guidelines committee, and as head of the Cervical screening process register. He has been a member of the National Board of health and welfare evaluation committee for the Cervical screening program. He has received no financial support or reimbursement from commercial companies for any activity. BJ has research grants from the Swedish Research Council, the Research Council of Norway, the March of Dimes, and the Burroughs Wellcome Fund. During the last five years, he has performed clinical diagnostic trials for Ariosa, Natera, Vanadis, and Hologic with reimbursement costs per recruited patient. He has conducted clinical trials on probiotics in pregnancy in collaboration with BioGaia and FukoPharma. He has also been involved in the IMPACT study where Roche and Thermo Fisher paid for PLGF-analyzes. He has also arranged scientific meetings with commercial partners (ESPBC 2016) and a Nordic educational meeting on NIPT and preeclampsia screening (2017). No lectures, travel, or personal reimbursements from the companies.

 * E-mail: johanna.wiik@gu.se 10 5 2021 5 2021 18 5 e1003641 27 12 2020 29 4 2021 2021 Wiik et al This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Background

Treatment of cervical intraepithelial neoplasia (CIN) is associated with an increased risk of preterm delivery (PTD) although the exact pathomechanism is not yet understood. Women with untreated CIN also seem to have an increased risk of PTD. It is unclear whether this is attributable to human papillomavirus (HPV) infection or other factors. We aimed to investigate whether HPV infection shortly before or during pregnancy, as well as previous treatment for CIN, is associated with an increased risk of PTD and other adverse obstetric and neonatal outcomes.

 Methods and findings

This was a retrospective population-based register study of women with singleton deliveries registered in the Swedish Medical Birth Register 1999–2016 (n = 1,044,023). The study population had a mean age of 30.2 years (SD 5.2) and a mean body mass index of 25.4 kg/m2 (SD 3.0), and 44% of the women were nulliparous before delivery. Study groups were defined based on cervical HPV tests, cytology, and histology, as registered in the Swedish National Cervical Screening Registry. Women with a history of exclusively normal cytology (n = 338,109) were compared to women with positive HPV tests (n = 2,550) or abnormal cytology (n = 11,727) within 6 months prior to conception or during the pregnancy, women treated for CIN3 before delivery (n = 23,185), and women with CIN2+ diagnosed after delivery (n = 33,760). Study groups were compared concerning obstetric and neonatal outcomes by logistic regression, and comparisons were adjusted for socioeconomic and health-related confounders. HPV infection was associated with PTD (adjusted odds ratio [aOR] 1.19, 95% CI 1.01–1.42, p = 0.042), preterm prelabor rupture of membranes (pPROM) (aOR 1.52, 95% CI 1.18–1.96, p < 0.001), prelabor rupture of membranes (PROM) (aOR 1.24, 95% CI 1.08–1.42, p = 0.002), and neonatal mortality (aOR 2.69, 95% CI 1.25–5.78, p = 0.011). Treatment for CIN was associated with PTD (aOR 1.85, 95% CI 1.76–1.95, p < 0.001), spontaneous PTD (aOR 2.06, 95% CI 1.95–2.17, p < 0.001), pPROM (aOR 2.36, 95% CI 2.19–2.54, p < 0.001), PROM (aOR 1.11, 95% CI 1.05–1.17, p < 0.001), intrauterine fetal death (aOR 1.35, 95% CI 1.05–1.72, p = 0.019), chorioamnionitis (aOR 2.75, 95% CI 2.33–3.23, p < 0.001), intrapartum fever (aOR 1.24, 95% CI 1.07–1.44, p = 0.003), neonatal sepsis (aOR 1.55, 95% CI 1.37–1.75, p < 0.001), and neonatal mortality (aOR 1.79, 95% CI 1.30–2.45, p < 0.001). Women with CIN2+ diagnosed within 3 years after delivery had increased PTD risk (aOR 1.18, 95% CI 1.10–1.27, p < 0.001). Limitations of the study include the retrospective design and the fact that because HPV test results only became available in 2007, abnormal cytology was used as a proxy for HPV infection.

 Conclusions

In this study, we found that HPV infection shortly before or during pregnancy was associated with PTD, pPROM, PROM, and neonatal mortality. Previous treatment for CIN was associated with even greater risks for PTD and pPROM and was also associated with PROM, neonatal mortality, and maternal and neonatal infectious complications.

In a retrospective analysis of population-based registry data, Johanna Wiik and colleagues investigate relationships between HPV infection, treatment for cervical intraepithelial neoplasia, and pregnancy and birth outcomes.

 Author summary Why was this study done?

Treatment of cervical intraepithelial neoplasia (CIN) is associated with an increased risk of preterm delivery (PTD), preterm prelabor rupture of the membranes (pPROM), and neonatal mortality. However, the exact biological mechanism is still unknown.

Women with untreated CIN also seem to have an increased risk of PTD. It is unknown whether HPV infection can cause PTD or other adverse obstetric outcomes.

Although ascending bacterial infection is an established leading cause of PTD, there is limited knowledge concerning whether PTD after excisional treatment for CIN is associated with infectious complications.

 What did the researchers do and find?

This retrospective population-based register study (1999–2016) found that HPV infection shortly before or during pregnancy is associated with an increased risk of PTD, pPROM, prelabor rupture of the membranes, and neonatal mortality.

Treatment for CIN was also associated with these adverse outcomes and with an even higher risk for PTD and pPROM.

This study presents new evidence that previous treatment for CIN is associated with an increased risk of maternal and neonatal infectious complications.

 What do these findings mean?

Although we cannot claim causality due to the register-based study design, our results suggest that pregnancies after treatment for CIN should be regarded as high-risk pregnancies and counseled accordingly.

These results support the idea that strategies to mitigate HPV infection, such as vaccination programs, may be beneficial for maternal and neonatal pregnancy outcomes.

 http://dx.doi.org/10.13039/501100010100 Sykehuset Østfold 16/04196 https://orcid.org/0000-0002-9441-2035 Wiik Johanna http://dx.doi.org/10.13039/501100003744 Stiftelsen Handlanden Hjalmar Svenssons HJSV2020079 https://orcid.org/0000-0002-9441-2035 Wiik Johanna http://dx.doi.org/10.13039/501100003745 Stiftelserna Wilhelm och Martina Lundgrens 2016-1005 https://orcid.org/0000-0002-3608-7430 Sengpiel Verena Fru Mary von Sydows, född Wijk, donationsfond nr 1016 https://orcid.org/0000-0002-3608-7430 Sengpiel Verena JW has received research grants from Østfold Hospital Trust, Norway (nr 16/04196) https://sykehuset-ostfold.no/helsefaglig/forskning, and Hjalmar Svenssons forskningsfond, Sweden (nr HJSV2020079) https://www.stiftelsemedel.se/stiftelsen-handlanden-hjalmar-svenssons-forskningsfond/. VS has received research grants from Wilhelm och Martina Lundgren Vetenskapsfond (2016-1005) https://wmlundgren.se/ and Fru Mary von Sydows, född Wijk, donationsfond (nr 1016) https://www.maryvonsydowstiftelsen.se/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. PLOS Publication Stage vor-update-to-uncorrected-proof Publication Update 2021-05-24 Data Availability Data cannot be shared publicly because the dataset is a collection of data from several Swedish national registers and we are not allowed to share it. The mandatory Swedish Medical Birth Register and the Swedish Cancer Registry are national datasets and therefore considered to be public property. Access to the data is given only to researchers with permission from a Swedish regional ethical review board (see https://www.etikprovningsmyndigheten.se) and after approval of the research plan by the data managers. Data access requests may be sent to the Swedish National Board of Health and Welfare (https://www.socialstyrelsen.se). After permission from a Swedish regional ethical review board, data researchers can also apply to access data from Statistics Sweden (https://www.scb.se) and the Swedish National Cervical Screening Registry (http://www.nkcx.se/). Introduction

Human papillomavirus (HPV) infection is the most common genital infection in women of reproductive age. Persistent genital infection with high-risk HPV is causally associated with cervical cancer and its precursor, cervical intraepithelial neoplasia (CIN) [1]. The widespread introduction of cervical cancer screening [2,3] and subsequent treatment of CIN has lowered the incidence of cervical cancer significantly [4]. Unfortunately, surgical excision to treat CIN has been associated with an increased risk of preterm delivery (PTD), preterm prelabor rupture of membranes (pPROM), conditions requiring neonatal intensive care, and neonatal mortality in subsequent pregnancies [5]. PTD, birth before 37 weeks of gestation, is an enormous global obstetric and societal problem, as it is the main cause of mortality in children under the age of 5 years, as well as of short- and long-term morbidity [6,7].

The mechanism behind excisional treatment increasing the risk of PTD remains unclear. The hypotheses include increased risk of ascending bacterial infection, HPV-induced immunomodulation, and acquired “mechanical weakness” secondary to loss of cervical tissue [8]. Although bacterial infection is an established major cause of PTD, especially early PTD and PTD starting with pPROM [9], there is limited knowledge concerning whether PTD after excisional treatment is associated with infectious complications [10].

The magnitude of the increase in risk for PTD attributed to treatment differs between studies [8,10–15] and seems to depend on the type of treatment. The risk increase is higher after excision than after ablation and is highest after cold knife excision [10]. Risk of PTD also seems to increase with the depth of excision [10]. Furthermore, the risk increase depends on whether healthy women or women with untreated CIN/HPV infection serve as the comparison group [10]. While it has been suggested during recent years that untreated CIN also confers a risk of PTD [8,16,17], a recent Cochrane review and meta-analysis concluded that further research is needed to understand the causal link and possible pathomechanism [10]. It is as yet unclear whether the pathomechanism is the HPV infection itself or whether the association between CIN and PTD is due to a vulnerability to both conditions, either by genetic predisposition or as a product of confounding [10,16]. It is thus unknown whether HPV infection can cause PTD or other adverse obstetric outcomes. Studies linking positive HPV tests and/or abnormal cervical cytology with obstetric outcomes have shown conflicting results [18–21]. A recent meta-analysis and systematic review suggested an association between HPV infection and PTD, and possibly pPROM [22], although all included studies were small. Other obstetric or neonatal outcomes in women with untreated CIN/HPV infection have not been studied in detail [10,17,23,24].

In summary, the risk of PTD increases after treatment for CIN, but the underlying mechanism is still not known. Women with untreated CIN also seem to have an increased risk of PTD, but it has not been established whether this risk is attributable to HPV infection during pregnancy. Neither the associations between untreated HPV infection in pregnancy and PTD and other obstetric and neonatal outcomes, nor the association between previous treatment for CIN and infectious pregnancy complications, have as yet been studied in a comprehensive population-based study. In this large Swedish national population-based study, we aimed to investigate whether HPV infection shortly before or during pregnancy is associated with an increased risk of PTD and other adverse obstetric and neonatal outcomes. We also aimed to study the association between previous treatment for CIN and PTD and other adverse obstetric and neonatal outcomes, with special focus on infectious complications at birth.

 Materials and methods Data sources

This study is a retrospective population-based study using data from different Swedish health and population registers. Data linkage between the registers was performed with the unique personal identification number held by each resident of Sweden. The Swedish Medical Birth Register (MBR), established in 1973 and managed by the Swedish National Board of Health and Welfare, is the object of compulsory registration and thus comprises all live births and stillbirths in Sweden at 22 completed weeks of gestation and up [25]. The information available in the register is extracted from antenatal and delivery unit medical records and includes data on maternal health, reproductive history, pregnancy complications and neonatal outcomes. The Swedish National Cervical Screening Registry (NKCx) contains data from 1978 onwards, with full national coverage of all cervical cytology results since 1997 and full national coverage of histology results since 1998 [26]. Cervical HPV tests have been recorded in the database since 2007. The Swedish Cancer Register, a mandatory registry established in 1958 and managed by the Swedish National Board of Health and Welfare, registers all diagnosed cancer cases in Sweden, as well as all cases of CIN3 [27]. Information on education level, country of birth, and income was obtained from the Swedish Register on Participation in Education [28], the Total Population Register [29], and the Income and Tax Assessment Register [30], managed by Statistics Sweden.

This study is reported as per the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline (S1 STROBE Checklist). The study was prospectively planned in 2015, the dataset was received in 2019, and analyses were conducted until November 2020. We did not publish the analysis plan, but the overall exposure, outcomes, confounders, and analyses were planned in 2015 by the research team based on hypotheses drawn from previous studies. After obtaining and reviewing the content of the dataset, but before starting the analyses, the final definition of study groups, outcomes, and study period was decided based on the available data and quality of the dataset. During the analysis process, we decided to also conduct stratified analyses.

 Study population

All women with singleton births between 1 January 1999 and 31 December 2016 were identified in the MBR. Women with a history of chronic inflammatory disease, human immunodeficiency virus infection, or organ transplantation were excluded (see S1 Table for the International Classification of Diseases [ICD] codes leading to exclusion), leaving a study population comprising 1,787,842 deliveries in 1,044,023 women with a mean age at delivery of 30.2 years (SD 5.2) and a mean body mass index (BMI) of 25.4 kg/m2 (SD 3.0); 44% of the women were nulliparous before delivery. Of these, 400,583 women had at least 1 delivery that fulfilled the criteria for inclusion in a study group (see below; Fig 1).

10.1371/journal.pmed.1003641.g001 Flowchart of the study population.

CIN, cervical intraepithelial neoplasia; HIV, human immunodeficiency virus; HPV, human papillomavirus.

 Exposures

A delivery registered in the MBR was eligible for inclusion in a study group if the woman fulfilled the criteria for exposure, i.e., results of a cervical HPV test registered in the NKCx in 2007–2016, cervical cytology or histology registered in the NKCx in 1978–2016, and/or a histological diagnosis registered in the Swedish Cancer Register. For exact classification of study groups, see S2 Table. For classification of cytology and histology results, see S3 Table.

A reference group was defined, consisting of women who had a history of exclusively normal cervical cytology results until the end of the study period and at least 1 sample taken in the 3 years preceding the included delivery (n = 338,109).

The exposure groups were defined as follows:

HPV infection group: women with presumed HPV infection during pregnancy, based on abnormal cervical cytology or positive HPV test recorded within 6 months prior to conception or during pregnancy. Two partly overlapping subgroups were defined:

HPV infection (cytology): abnormal cytology (n = 11,727).

HPV infection (HPV test): positive cervical HPV test (n = 2,550).

Subsequent CIN2+ group: at presumed risk of persistent HPV infection based on a histological diagnosis of CIN2 or CIN3, adenocarcinoma in situ (AIS), or cervical cancer any time after delivery (n = 33,760).

Treated group: histologically diagnosed CIN3 before conception. Since there is no national Swedish register covering treatment for CIN, CIN3 was used as a proxy for treatment as these women are always treated in Sweden, a policy that has been consistent over the study period (n = 23,185).

In order to avoid women previously treated for CIN being included in the HPV infection groups or the subsequent CIN2+ group, women with histologically diagnosed CIN1 more than once or with CIN2+ before the pertinent delivery were excluded from these groups.

Three different treatment periods, based on the year of first diagnosis of CIN3, were defined, corresponding to differences in predominant mode of treatment: 1978–1985 (cold knife conization), 1986–1995 (tissue-saving methods such as cryotherapy, laser vaporization, laser conization, and diathermy), and 1996–2016 (large loop excision of the transformation zone [LLETZ], also referred to as loop electrosurgical excision procedure [LEEP]) [31].

In the treated group, the interval from treatment to delivery was determined, as was the interval from delivery to CIN2+ diagnosis in the subsequent CIN2+ group.

 Outcomes

The primary outcome was PTD at 22–36 weeks of gestation (154–258 days). Gestational age was retrieved from the MBR using the best estimate, i.e., ultrasound determination when available and last menstrual period or estimation of gestational age at delivery ward in the remaining cases. Subanalyses for early PTD (22–33 weeks, or 154–237 days, of gestation) and for very early PTD (22–27 weeks, or 154–195 days, of gestation) were performed.

Secondary outcomes were pPROM (determined according to ICD-10 codes in the MBR) and spontaneous PTD (defined as pPROM or preterm labor, excluding deliveries that started with induction or cesarean section, according to ICD-10 codes and MBR parameters).

Further studied outcomes comprised prelabor rupture of membranes (PROM) in term pregnancies (≥37 weeks of gestation), chorioamnionitis, intrapartum fever, neonatal sepsis, Apgar score < 7 at 5 minutes, intrauterine fetal death, neonatal mortality (1–28 days), and small for gestational age (SGA), defined as birthweight less than −2 SD according to the Swedish reference curves [32] (S4 Table).

 Background variables

The following background variables were retrieved from the MBR and from Statistics Sweden registers: age at delivery, BMI, smoking before and during pregnancy, marital status, education level at delivery, employment at delivery, disposable household income in the 3 years preceding delivery, country of birth, parity, infant’s sex, and assisted reproduction, as well as chronic renal disease, diabetes, epilepsy, and chronic hypertension as reported in antenatal care records.

 Statistical analyses

Descriptive data are presented as number and percentage for categorical variables and as mean (SD) and median (interquartile range) for continuous variables. Analyses were performed using R (version 4.0.0; R Foundation for Statistical Computing, Vienna, Austria; https://www.r-project.org/) and SPSS software (version 26.0; IBM; https://www.ibm.com/analytics/spss-statistics-software). A significance level of 0.05 was applied throughout.

The study groups were compared concerning obstetric and neonatal outcomes by unadjusted and adjusted logistic regression analysis. If a woman had several deliveries that fulfilled the criteria for inclusion in a group, only 1 delivery was included. A random delivery in the reference group was compared to the first eligible delivery after treatment in the treated group and the last eligible delivery in the HPV infection groups (cytology and HPV test) and the last delivery before diagnosis of CIN2+ in the subsequent CIN2+ group. The first eligible delivery after treatment in the treated group was compared to the last delivery in a woman included in the other exposure groups. This was done to better match for age and parity, since women in the treated group naturally were older than women in the other exposure groups. Women who had both a delivery after treatment and a previous delivery included in any of the other exposure groups were excluded from the treated group when the treated group was compared to the other exposure groups.

HPV infection can exist for a long time before diagnosis of CIN2+. Therefore, the subsequent CIN2+ group was compared to the reference group after stratification for interval (0–3 years or >3 years) to diagnosis of CIN2+, based on the median interval from delivery to CIN2+ diagnosis of 3.2 years. The 2 groups were also compared with each other.

Women with a delivery included in the subsequent CIN2+ group followed by a delivery included in the treated group were included in paired analyses with conditional logistic regression analysis.

When comparing the HPV infection (HPV test) group with other groups, only deliveries after 2006 were included, since no HPV tests were registered before that year. In order to test whether cytology was a valid substitute for a positive HPV test, the 2 HPV infection groups were compared to each other. In these analyses, women with both a positive HPV test and abnormal cytology were excluded from the HPV infection (cytology) group.

The multivariable analyses were adjusted for potential confounding factors, including background variables with an uneven distribution between the groups, i.e., year of delivery (1999–2001, 2002–2004, 2005–2007, 2008–2010, 2011–2013, 2014–2016), maternal age (<21, 21–25, 26–30, 31–35, 36–40, >40), parity (0, 1, 2, 3, >3), BMI (underweight [<18.5 kg/m2], normal weight [18.5–24.9 kg/m2], overweight [25.0–29.9 kg/m2], obese ≥30.0 kg/m2], missing), marital status (cohabiting, single, other, missing), country of birth (Sweden, Europe, Asia, America/Oceania, Africa, missing), infant’s sex (boy, girl, missing), smoking (never, before pregnancy, in early pregnancy, in the third trimester, missing), highest disposable household income in the 3 years preceding delivery (population divided into tertiles for every year), education level (primary, secondary, post-secondary < 3 years, post-secondary ≥ 3 years, missing), and assisted reproduction (yes, no). The paired analyses were adjusted for BMI, marital status, infant’s sex, smoking, and assisted reproduction, with the group definitions defined above.

In order to study the implication of infectious complications, the treated group was compared with the reference group regarding chorioamnionitis and neonatal sepsis, with adjusted logistic regression after stratification for PTD. The treated group was also compared with the reference group regarding chorioamnionitis and neonatal sepsis in PTD cases, after stratification for pPROM and also adjusted for gestational age.

Neonatal mortality in the treated and HPV infection groups was compared with that in the reference group, with adjusted logistic regression analysis also including PTD in the adjustments. Subgroup analysis comparing neonatal mortality in the treated and reference groups was also performed, after stratification for infectious complications (chorioamnionitis and/or neonatal sepsis) and also adjusted for gestational age.

In all stratified analyses, differences in odds ratios between strata were analyzed by an interaction term between the stratum and the group in logistic regression.

 Ethics statement

The study was approved by the Regional Ethical Review Board at the University of Gothenburg (registration number 614–15). In this retrospective register-based study, no consent was obtained from the participants since the data were analyzed anonymously.

 Results Characteristics of the study population

Background factors for the study population are presented in Table 1. The study groups differed, for example regarding age, parity, and smoking. In the reference group, 10% (n = 32,457 women) were older than 35 years, and similarly 10% in the subsequent CIN2+ group (n = 3,492) and 12% in the HPV infection (cytology) group (n = 1,366) were older than 35 years, while age over 35 years was more frequent in the HPV infection (HPV test) group (n = 429, 17%) and the treated group (n = 4,755, 21%). Nulliparity was most frequent in the treated group (n = 13,425, 58%) and HPV infection groups (cytology, n = 6,479, 55%; HPV test, n = 1,481, 58%) and less frequent in the reference group (n = 163,533, 48%) and subsequent CIN2+ group (n = 12,730, 38%). Smoking during pregnancy was less common in the reference group (n = 15,365, 4.5%) than the exposure groups (HPV infection [cytology], n = 1,471, 12.5%; HPV infection [HPV test], n = 177, 6.9%; treated, n = 2,811, 12.1%; subsequent CIN2+, n = 5,895, 17.5%).

10.1371/journal.pmed.1003641.t001 Demographics and clinical characteristics in the study groups.
Characteristics Reference group(n = 338,109) HPV infection groups Treated group(n = 23,185) Subsequent CIN2+ group(n = 33,760)
Cytology(n = 11,727) HPV test(n = 2,550)
Age at delivery (years)
<21 858 (0.3) 161 (1.4) 12 (0.5) 10 (0.0) 1,205 (3.6)
21–25 54,778 (16.2) 2,673 (22.8) 445 (17.5) 1,276 (5.5) 7,402 (21.9)
26–30 148,021 (43.8) 4,447 (37.9) 875 (34.3) 7,865 (33.9) 12,099 (35.8)
31–35 101,995 (30.2) 3,080 (26.3) 789 (30.9) 9,279 (40.0) 9,562 (28.3)
36–40 29,344 (8.7) 1,177 (10.0) 368 (14.4) 4,095 (17.7) 3,144 (9.3)
>40 3,113 (0.9) 189 (1.6) 61 (2.4) 660 (2.8) 348 (1.0)
BMI class (kg/m2)
Underweight (<18.5) 6,886 (2.0) 326 (2.8) 79 (3.1) 376 (1.6) 882 (2.6)
Normal weight (18.5–24.9) 193,930 (57.4) 6,871 (58.6) 1,587 (62.2) 13,678 (59.0) 19,233 (57.0)
Overweight (25–29.9) 76,964 (22.8) 2,461 (21.0) 499 (19.6) 5,153 (22.2) 7,348 (21.8)
Obese (≥30) 34,493 (10.2) 1,160 (9.9) 253 (9.9) 1,868 (8.1) 2,935 (8.7)
Missing 25,836 (7.6) 909 (7.8) 132 (5.2) 2,110 (9.1) 3,362(10.0)
Smoking
Never 286,236 (84.7) 8,582 (73.2) 2,057 (80.7) 16,735 (72.2) 22,151 (65.6)
Before pregnancy 25,166 (7.4) 1,327 (11.3) 260 (10.2) 2,727 (11.8) 4,415 (13.1)
In early pregnancy 6,254 (1.8) 530 (4.5) 56 (2.2) 1,079 (4.7) 2,102 (6.2)
In the third trimester 9,111 (2.7) 941 (8.0) 121 (4.7) 1,732 (7.5) 3,793 (11.2)
Missing 11,342 (3.4) 347 (3.0) 56 (2.2) 912 (3.9) 1,299 (3.8)
Infant’s sex
Boy 174,095 (51.5) 6,108 (52.1) 1,322 (51.8) 11,853 (51.1) 17,297 (51.2)
Girl 164,000 (48.5) 5,618 (47.9) 1,228 (48.2) 11,331 (48.9) 16,462 (48.8)
Missing 14 1 0 1 1
Assisted reproduction1 9,341 (2.8) 153 (1.3) 46 (1.8) 934 (4.0) 434 (1.3)
Employment
Full-time 181,520 (53.7) 5,728 (48.8) 1,458 (57.2) 14,315 (61.7) 14,719 (43.6)
Part-time 79,475 (23.5) 2,469 (21.1) 438 (17.2) 4,278 (18.5) 8,390 (24.9)
None 47,200 (14.0) 2,388 (20.4) 449 (17.6) 2,359 (10.2) 6,605 (19.6)
Missing 29,914 (8.8) 1,142 (9.7) 205 (8.0) 2,233 (9.6) 4,046 (12.0)
Parity
0 163,533 (48.4) 6,479 (55.2) 1,481 (58.1) 13,425 (57.9) 12,730 (37.7)
1 129,737 (38.4) 3,407 (29.1) 724 (28.4) 5,968 (25.7) 14,547 (43.1)
2 36,004 (10.6) 1,308 (11.2) 257 (10.1) 2,788 (12.0) 4,826 (14.3)
3 6,780 (2.0) 354 (3.0) 54 (2.1) 751 (3.2) 1,187 (3.5)
>3 2,055 (0.6) 179 (1.5) 34 (1.3) 253 (1.1) 470 (1.4)
Marital status
Cohabiting 312,277 (92.4) 10,286 (87.7) 2,252 (88.3) 20,777 (89.6) 29,551 (87.5)
Single 3,625 (1.1) 346 (3.0) 63 (2.5) 443 (1.9) 1,007 (3.0)
Other 7,369 (2.2) 626 (5.3) 126 (4.9) 792 (3.4) 1,605 (4.8)
Missing 14,838 (4.4) 469 (4.0) 109 (4.3) 1,173 (5.1) 1,597 (4.7)
Concurrent disease2
Renal disease 1,326 (0.4) 63 (0.5) 17 (0.7) 110 (0.5) 184 (0.5)
Diabetes 1,864 (0.6) 69 (0.6) 14 (0.5) 104 (0.4) 144 (0.4)
Epilepsy 1,519 (0.4) 66 (0.6) 15 (0.6) 121 (0.5) 176 (0.5)
Chronic hypertension 1,218 (0.4) 39 (0.3) 12 (0.5) 99 (0.4) 108 (0.3)
Education level3
Primary school, up to 9 years 20,947 (6.2) 1,439 (12.3) 234 (9.2) 1,798 (7.8) 4,820 (14.3)
Secondary 136,656 (40.4) 5,329 (45.54) 967 (37.9) 10,092 (43.5) 17,386 (51.5)
Post-secondary < 3 years 46,648 (13.8) 1,525 (13.0) 358 (14.0) 3,438 (14.8) 4,007 (11.9)
Post-secondary ≥ 3 years 132,012 (39.0) 3,294 (28.1) 971 (38.1) 7,806 (33.7) 7,148 (21.2)
Missing 1,846 (0.5) 140 (1.2) 20 (0.8) 51 (0.2) 399 (1.2)
Country of birth
Sweden 290,269 (85.9) 9,597 (81.8) 2,053 (80.5) 21,395 (92.3) 29,724 (88.0)
Europe 20,091 (5.9) 872 (7.4) 181 (7.1) 1,017 (4.4) 2,233 (6.6)
Asia 19,105 (5.7) 784 (6.7) 188 (7.4) 495 (2.1) 1,213 (3.6)
America/Oceania 3,253 (1.0) 167 (1.4) 47 (1.8) 207 (0.9) 381 (1.1)
Africa 5,297 (1.6) 297 (2.5) 80 (3.1) 70 (0.3) 203 (0.6)
Missing 94 (0) 10 (0.1) 1 (0.0) 1 (0) 6 (0.0)
Year of delivery
1999–2001 37,540 (11.1) 1,346 (11.5) 0 3,097 (13.4) 6,389 (18.9)
2002–2004 39,384 (11.6) 1,250 (10.7) 0 3,268 (14.1) 6,372 (18.9)
2005–2007 43,310 (12.8) 1,198 (10.2) 5 (0.2) 3,368 (14.5) 6,595 (19.5)
2008–2010 53,847 (15.9) 1,544 (13.2) 76 (3.0) 3,872 (16.7) 6,566 (19.4)
2011–2013 66,932 (19.8) 2,533 (21.6) 542 (21.3) 4,259 (18.4) 5,494 (16.3)
2014–2016 97,096 (28.7) 3,856 (32.9) 1,927 (75.6) 5,321 (23.0) 2,344 (6.9)
Highest disposable household income in 3 years preceding delivery
Lowest tertile 44,834 (13.3) 2,674 (22.8) 610 (23.9) 2,555 (11.0) 6,320 (18.7)
Middle tertile 100,738 (29.8) 3,882 (33.1) 758 (29.7) 6,217 (26.8) 11,007 (32.6)
Highest tertile 192,535 (56.9) 5,171 (44.1) 1,181 (46.3) 14,413 (62.2) 16,426 (48.7)
Gestational age estimation method
Ultrasound 309,355 (91.5) 10,828 (92.3) 2,429 (95.3) 20,836 (89.9) 30,148 (89.3
Last menstrual period 15,200 (4.5) 474 (4.0) 45 (1.8) 1,230 (5.3) 2,024 (6.0)
Other4 13,554 (4.0) 425 (3.6) 76 (3.0) 1,119 (4.8) 1,588 (4.7)
Cytology diagnosis
Low grade 9,916 (84.6)
High grade 1,811 (15.4)
Time period of CIN3 diagnosis
1978–1985 76 (0.3)
1986–1995 2,467 (10.6)
1996–2016 20,642 (89.0)
Interval from CIN3 diagnosis to delivery (years)
Mean (SD) 4.4 (3.4)
Median (IQR) 3.4 (1.9–6.1)
Interval from delivery to diagnosis of CIN2/CIN3/AIS/cancer (years)
Mean (SD) 4.3 (3.7)
Median (IQR) 3.2 (1.4–6.2)

Data are presented as number (percentage) unless otherwise specified. Percentages are based on those with available data. Percentages of missing are based on the total numbers.

1Treatment to achieve pregnancy.

2As reported in antenatal care records. Missing values were interpreted as the woman not having any concurrent disease, in accordance with how data are registered in antenatal care records.

3Highest education level at time of delivery.

4Ultrasound, last menstrual period, and/or estimation of gestational age at delivery ward.

AIS, adenocarcinoma in situ; BMI, body mass index; CIN, cervical intraepithelial neoplasia; IQR, interquartile range; SD, standard deviation.

The comparisons presented below for different obstetric outcomes are adjusted logistic regression analyses; unadjusted analyses are presented in S5–S7 Tables.

 Preterm delivery

In the total dataset of 1,787,842 deliveries in 1,044,023 women, 87,727 deliveries (4.9%) were PTD and 62,951 deliveries were spontaneous PTD (3.5%).

Compared to the reference group (4.6%), the treated group had the highest risk of PTD (9.1%, adjusted odds ratio [aOR] 1.85, 95% CI 1.76–1.95, p < 0.001), but an increased risk was also found in the HPV infection (cytology) group (5.9%, aOR 1.21, 95% CI 1.12–1.31, p < 0.001) and the HPV infection (HPV test) group (5.6%, aOR 1.19, 95% CI 1.01–1.42, p = 0.042) (Table 2; Fig 2A). These results were similar for spontaneous PTD; the treated group had aOR 2.06 (95% CI 1.95–2.17, p < 0.001) and the HPV infection (cytology) group had aOR 1.18 (95% 1.07–1.29, p = 0.001) (Table 2; Fig 2B). The treated group and the HPV infection (cytology) group also had increased risk of very early and early PTD (Table 2).

10.1371/journal.pmed.1003641.g002 Risk of preterm delivery and spontaneous preterm delivery—adjusted logistic regression.

Preterm delivery (2a); spontaneous preterm delivery (2b). Women with HPV infection had an increased risk of preterm delivery and spontaneous preterm delivery; treatment increased the risk further. aORs are given, with 95% confidence intervals in parentheses. Analyses adjusted for year of delivery, maternal age, parity, BMI, marital status, country of birth, infant’s sex, smoking, income, education level, and assisted reproduction. aOR, adjusted odds ratio; CIN, cervical intraepithelial neoplasia; HPV, human papillomavirus.

 10.1371/journal.pmed.1003641.t002 Obstetric and neonatal outcomes in exposure groups compared to the reference group—adjusted multivariable logistic regression analyses.
Outcome Reference group (n = 338,109) HPV infection groups Treated group (n = 23,185) Subsequent CIN2+ group (n = 33,760)
Cytology (n = 11,727) HPV test (n = 2,550)
n (%) n (%) aOR (95% CI) p-Value n (%) aOR1 (95% CI) p-Value n (%) aOR (95% CI) p-Value n (%) aOR (95% CI) p-Value
PTD, <37 weeks 15,661 (4.6) 692 (5.9) 1.21 (1.12–1.31) <0.001 143 (5.6) 1.19 (1.01–1.42) 0.042 2,106 (9.1) 1.85 (1.76–1.95) <0.001 1,736 (5.1) 1.12 (1.06–1.18) <0.001
Early PTD, <34 weeks 4,221 (1.2) 221 (1.9) 1.39 (1.21–1.60) <0.001 34 (1.3) 0.99 (0.70–1.40) 0.96 661 (2.9) 2.02 (1.86–2.21) <0.001 488 (1.4) 1.18 (1.06–1.30) 0.002
Very early PTD, <28 weeks 820 (0.2) 55 (0.5) 1.73 (1.31–2.28) <0.001 7 (0.3) 0.97 (0.46–2.06) 0.94 139 (0.6) 2.20 (1.82–2.66) <0.001 87 (0.3) 1.10 (0.87–1.39) 0.42
Spontaneous PTD 11,409 (3.4) 493 (4.2) 1.18 (1.07–1.29) 0.001 100 (3.9) 1.17 (0.95–1.43) 0.14 1,699 (7.3) 2.06 (1.95–2.17) <0.001 1,291 (3.8) 1.14 (1.07–1.21) <0.001
pPROM 5,110 (1.5) 232 (2.0) 1.22 (1.07–1.40) 0.004 64 (2.5) 1.52 (1.18–1.96) 0.001 934 (4.0) 2.36 (2.19–2.54) <0.001 521 (1.5) 1.09 (0.99–1.20) 0.09
PROM in deliveries at ≥37 weeks 21,906 (6.8) 828 (7.5) 1.06 (0.98–1.14) 0.13 251 (10.4) 1.24 (1.08–1.42) 0.002 1,772 (8.4) 1.11 (1.05–1.17) <0.001 1,719 (5.4) 0.99 (0.94–1.04) 0.64
SGA2 6,873 (2.0) 320 (2.7) 1.09 (0.97–1.22) 0.16 65 (2.6) 0.96 (0.75–1.24) 0.76 594 (2.6) 1.02 (0.94–1.12) 0.64 715 (2.1) 0.99 (0.91–1.07) 0.72
Apgar score < 7 at 5 minutes 4,165 (1.2) 191 (1.6) 1.20 (1.04–1.40) 0.014 41 (1.6) 1.04 (0.76–1.43) 0.79 366 (1.6) 1.14 (1.02–1.27) 0.019 323 (1.0) 0.89 (0.79–1.00) 0.043
Neonatal mortality 343 (0.1) 24 (0.2) 1.81 (1.19–2.76) 0.006 7 (0.3) 2.69 (1.25–5.78) 0.011 47 (0.2) 1.79 (1.30–2.45) <0.001 29 (0.1) 0.71 (0.47–1.05) 0.09
Intrauterine fetal death 711 (0.2) 43 (0.4) 1.55 (1.13–2.12) 0.006 6 (0.2) 0.93 (0.41–2.09) 0.86 74 (0.3) 1.35 (1.05–1.72) 0.019 50 (0.1) 0.71 (0.53–0.96) 0.026
Chorioamnionitis 895 (0.3) 45 (0.4) 1.25 (0.92–1.69) 0.15 10 (0.4) 1.00 (0.53–1.88) 1.00 196 (0.8) 2.75 (2.33–3.23) <0.001 74 (0.2) 1.02 (0.80–1.31) 0.85
Intrapartum fever 2,189 (0.6) 87 (0.7) 1.01 (0.82–1.26) 0.90 37 (1.5) 1.40 (1.00–1.96) 0.050 213 (0.9) 1.24 (1.07–1.44) 0.003 133 (0.4) 0.89 (0.74–1.06) 0.19
Neonatal sepsis 2,508 (0.7) 97 (0.8) 0.99 (0.80–1.21) 0.89 14 (0.6) 0.67 (0.40–1.14) 0.14 300 (1.3) 1.55 (1.37–1.75) <0.001 216 (0.6) 0.86 (0.74–0.99) 0.041

Statistically significant p-values in bold. Analyses adjusted for year of delivery, maternal age, parity, BMI, marital status, country of birth, infant’s sex, smoking, income, education level, and assisted reproduction.

1Analyses compared to reference group 2007–2016.

2Missing data: reference group, n = 575; HPV infection (cytology) group, n = 24; HPV infection (HPV test) group, n = 3; treated group, n = 47; subsequent CIN2+ group, n = 71.

aOR, adjusted odds ratio; CI, confidence interval; CIN, cervical intraepithelial neoplasia; HPV, human papillomavirus; pPROM, preterm prelabor rupture of membranes; PROM, prelabor rupture of membranes; PTD, preterm delivery; SGA, small for gestational age.

Women in the subsequent CIN2+ group also had a slightly increased risk of PTD (5.1%, aOR 1.12, 95% CI 1.06–1.18, p < 0.001) and spontaneous PTD (Table 2). However, when it came to the analyses stratified for interval from delivery to diagnosis, the increase was only significant for women diagnosed with CIN2+ within the first 3 years after delivery (Table 3). In comparison with the other exposure groups (rather than with the reference group), the treated group exhibited an increased risk of both PTD and spontaneous PTD (Table 4; Fig 2).

10.1371/journal.pmed.1003641.t003 Obstetric and neonatal outcomes in the subsequent CIN2+ group compared with the reference group, stratified for interval from delivery to CIN2+ diagnosis—adjusted multivariable logistic regression analyses.
Outcome Reference group(n = 338,109) Subsequent CIN2+ group Comparison of subsequent CIN2+ ≤3 years and >3 years after delivery
≤3 years after delivery (n = 16,152) >3 years after delivery1 (n = 17,608)
n (%) n (%) aOR (95% CI)2 p-Value n (%) aOR (95% CI)2 p-Value p-Value
PTD, <37 weeks 15,661 (4.6) 890 (5.5) 1.18 (1.10–1.27) <0.001 846 (4.8) 1.06 (0.99–1.15) 0.11 0.038
Early PTD, <34 weeks 4,221 (1.2) 249 (1.5) 1.22 (1.07–1.39) 0.003 239 (1.4) 1.13 (0.99–1.30) 0.08 0.44
Very early PTD, <28 weeks 820 (0.2) 45 (0.3) 1.13 (0.84–1.54) 0.42 42 (0.2) 1.07 (0.77–1.48) 0.71 0.78
Spontaneous PTD 11,409 (3.4) 665 (4.1) 1.20 (1.11–1.30) <0.001 626 (3.6) 1.07 (0.98–1.16) 0.14 0.038
pPROM 5,110 (1.5) 288 (1.8) 1.17 (1.04–1.33) 0.010 233 (1.3) 0.99 (0.86–1.14) 0.88 0.06
PROM in deliveries at ≥37 weeks 21,906 (6.8) 927 (6.1) 0.98 (0.92–1.05) 0.65 792 (4.7) 0.99 (0.92–1.07) 0.82 0.89
SGA3 6,873 (2.0) 355 (2.2) 0.98 (0.88–1.10) 0.78 360 (2.1) 0.99 (0.88–1.11) 0.84 0.96
Apgar score < 7 at 5 minutes 4,165 (1.2) 177 (1.1) 0.93 (0.80–1.09) 0.39 146 (0.8) 0.83 (0.70–0.98) 0.032 0.29
Neonatal mortality 343 (0.1) 17 (0,1) 0.95 (0.58–1.55) 0.82 12 (0.1) 0.51 (0.28–0.93) 0.027 0.10
Intrauterine fetal death 711 (0.2) 34 (0.2) 0.99 (0.70–1.41) 0.97 16 (0.1) 0.44 (0.26–0.73) 0.001 0.007
Chorioamnionitis 895 (0.3) 40 (0.2) 1.03 (0.75–1.42) 0.86 34 (0.2) 1.02 (0.71–1.46) 0.93 0.96
Intrapartum fever 2,189 (0.6) 83 (0.5) 0.93 (0.75–1.17) 0.54 50 (0.3) 0.81 (0.61–1.09) 0.17 0.46
Neonatal sepsis 2,508 (0.7) 124 (0.8) 1.00 (0.83–1.20) 0.96 92 (0.5) 0.71 (0.57–0.89) 0.003 0.018

Statistically significant p-values in bold. Analyses adjusted for year of delivery, maternal age, parity, BMI, marital status, country of birth, infant’s sex, smoking, income, education level, and assisted reproduction.

1Up to 18 years after delivery.

2Comparison with reference group.

3Missing data: reference group, n = 575; subsequent CIN2+ ≤3 years after delivery, n = 25; subsequent CIN2+ >3 years after delivery, n = 46.

aOR, adjusted odds ratio; CI, confidence interval; CIN, cervical intraepithelial neoplasia; HPV, human papillomavirus; pPROM, preterm prelabor rupture of membranes; PROM, prelabor rupture of membranes; PTD, preterm delivery; SGA, small for gestational age.

 10.1371/journal.pmed.1003641.t004 Obstetric and neonatal outcomes in the treated group compared to the HPV infection groups and the subsequent CIN2+group—adjusted multivariable logistic regression analyses.

.

Outcome Treated versus HPV infection (cytology) comparison Treated versus HPV infection (HPV test) comparison Treated versus subsequent CIN2+ comparison
Treated group (n = 22,711) HPV infection (cytology) group (n = 11,727) Treated group (n = 14,579) HPV infection (HPV test) group (n = 2,550) Treated group, (n = 18,505) Subsequent CIN2+ group (n = 33,760)
n (%) n (%) aOR (95% CI) p-Value n (%) n (%) aOR1 (95% CI) p-Value n (%) n (%) aOR (95% CI) p-Value
PTD, <37 weeks 2,066 (9.1) 692 (5.9) 1.61 (1.46–1.78) <0.001 1,313 (9.0) 143 (5.6) 1.68 (1.39–2.03) <0.001 1,751 (9.5) 1,736 (5.1) 1.77 (1.63–1.92) <0.001
Early PTD, <34 weeks 645 (2.8) 221 (1.9) 1.53 (1.29–1.81) <0.001 416 (2.9) 34 (1.3) 2.18 (1.50–3.17) <0.001 554 (3.0) 488 (1.4) 1.85 (1.59–2.13) <0.001
Very early PTD, <28 weeks 136 (0.6) 55 (0.5) 1.32 (0.93–1.87) 0.12 98 (0.7) 7 (0.3) 2.79 (1.23–6.35) 0.014 118 (0.6) 87 (0.3) 2.01 (1.44–2.80) <0.001
Spontaneous PTD 1,669 (7.3) 493 (4.2) 1.85 (1.65–2.07) <0.001 1,038 (7.1) 100 (3.9) 1,86 (1.49–2.33) <0.001 1,421 (7.7) 1,291 (3.8) 2.00 (1.82–2.19) <0.001
pPROM 918 (4.0) 232 (2.0) 2.09 (1.78–2.45) <0.001 598 (4.1) 64 (2.5) 1.55 (1.17–2.04) 0.002 779 (4.2) 521 (1.5) 2.51 (2.20–2.87) <0.001
PROM in deliveries at ≥37 weeks 1,752 (8.5) 828 (7.5) 1.08 (0.98–1.18) 0.12 1,208 (9.1) 251 (10.4) 0.88 (0.75–1.03) 0.11 1,526 (9.1) 1,719 (5.4) 1.21 (1.11–1.31) <0.001
SGA2 587 (2.6) 320 (2.7) 0.86 (0.74–1.01) 0.06 383 (2.6) 65 (2.6) 0.93 (0.70–1.25) 0.64 523 (2.8) 715 (2.1) 1.03 (0.90–1.17) 0.72
Apgar score <7 at 5 minutes 355 (1.6) 191 (1.6) 0.94 (0.78–1.14) 0.55 248 (1.7) 41 (1.6) 1.16 (0.81–1.67) 0.43 303 (1.6) 323 (1.0) 1.30 (1.08–1.57) 0.005
Neonatal mortality 43 (0.2) 24 (0.2) 1.04 (0.59–1.83) 0.89 21 (0.1) 7 (0.3) 0.56 (0.21–1.45) 0.23 35 (0.2) 29 (0.1) 2.61 (1.45–4.70) 0.001
Intrauterine fetal death 71 (0.3) 43 (0.4) 0.72 (0.48–1.09) 0.12 51 (0.3) 6 (0.2) 1.21 (0.49–3.00) 0.69 58 (0.3) 50 (0.1) 1.75 (1.13–2.73) 0.013
Chorioamnionitis 192 (0.8) 45 (0.4) 2.21 (1.55–3.15) <0.001 119 (0.8) 10 (0.4) 2.47 (1.24–4.91) 0.010 160 (0.9) 74 (0.2) 3.33 (2.41–4.60) <0.001
Intrapartum fever 211 (0.9) 87 (0.7) 1.21 (0.92–1.59) 0.17 154 (1.1) 37 (1.5) 0.79 (0.53–1.17) 0.24 197 (1.1) 133 (0.4) 1.37 (1.06–1.77) 0.015
Neonatal sepsis 294 (1.3) 97 (0.8) 1.61 (1.25–2.07) <0.001 171 (1.2) 14 (0.5) 2.34 (1.30–4.24) 0.005 257 (1.4) 216 (0.6) 2.02 (1.63–2.51) <0.001

Statistically significant p-values in bold. Analyses adjusted for year of delivery, maternal age, parity, BMI, marital status, country of birth, infant’s sex, smoking, income, education level, and assisted reproduction.

1Analyses 2007–2016.

2Missing data: treated group, n = 47; HPV infection (cytology) group, n = 24; HPV infection (HPV test) group, n = 3; subsequent CIN2+ group, n = 71.

aOR, adjusted odds ratio; CI, confidence interval; CIN, cervical intraepithelial neoplasia; HPV, human papillomavirus; pPROM, preterm prelabor rupture of membranes; PROM, prelabor rupture of membranes; PTD, preterm delivery; SGA, small for gestational age.

 Preterm prelabor rupture of membranes

In the study population, 27,687 deliveries started with pPROM (1.5%). Compared to the reference group (1.5%), the risk of pPROM was increased in the treated group (4.0%, aOR 2.36, 95% CI 2.19–2.54, p < 0.001), the HPV infection (cytology) group (2.0%, aOR 1.22, 95% CI 1.07–1.40, p = 0.004), and the HPV infection (HPV test) group (2.5%, aOR 1.52, 95% CI 1.18–1.96, p = 0.001) (Table 2; Fig 3). Women in the subsequent CIN2+ group did not have an increased risk of pPROM compared to the reference group (Table 2), although an increased risk was found if the women were diagnosed with CIN2+ within the first 3 years after delivery (Table 3). Compared with the other exposure groups, the treated group had an increased risk of pPROM (Table 4; Fig 3).

10.1371/journal.pmed.1003641.g003 Risk of pPROM—adjusted logistic regression.

Women with HPV infection had an increased risk of pPROM; treatment increased the risk further. aORs are given, with 95% confidence intervals in parentheses. Analyses adjusted for year of delivery, maternal age, parity, BMI, marital status, country of birth, infant’s sex, smoking, income, education level, and assisted reproduction. aOR, adjusted odds ratio; CIN, cervical intraepithelial neoplasia; HPV, human papillomavirus; pPROM, preterm prelabor rupture of membranes.

 PROM in term pregnancies

Of the 1,700,115 term pregnancies, a total of 111,519 deliveries started with PROM (6.6%). Women in the treated group had an increased risk of PROM at term compared to the reference group (8.4% versus 6.8%, aOR 1.11, 95% CI 1.05–1.17, p < 0.001) (Table 2) and compared to the subsequent CIN2+ group (aOR 1.20, 95% CI 1.11–1.31, p < 0.001) (Table 4). Moreover, the HPV infection (HPV test) group had an increased risk of PROM compared to the reference group (aOR 1.24, 95% CI 1.08–1.42, p = 0.002). The associations for the HPV infection (cytology) group were oriented in the same direction but were not statistically significant (Table 2).

 SGA and Apgar score

In the study population, 41,323 infants were born SGA (2.3%). Data were missing for 4,028 deliveries (0.2%). There was no difference between the reference group and any of the exposure groups in regard to SGA risk (Table 2).

In the study population, 22,968 babies were born with a 5-minute Apgar score < 7 (1.3%). The treated group had higher risk of low Apgar score compared to the reference group (Table 2) and to the subsequent CIN2+ group (Table 4). Furthermore, the HPV infection (cytology) group had an increased risk of low Apgar score. The association was oriented in the same direction in the HPV infection (HPV test) group but did not reach significance (Table 2).

 Intrauterine fetal death

There were 5,649 (0.3%) reported cases of intrauterine fetal death in the study population. Compared to the reference group (0.2%), the risk was increased in the HPV infection (cytology) group (0.4%, aOR 1.55, 95% CI 1.13–2.12, p = 0.006) and in the treated group (0.3%, aOR 1.35, 95% CI 1.05–1.72, p = 0.019), while it was decreased in the subsequent CIN2+ group (0.1%, aOR 0.71, 95% CI 0.53–0.96, p = 0.026) (Table 2). This decreased risk was significant for the subsequent CIN2+ subgroup of women who were diagnosed >3 years after delivery (Table 3).

 Infectious complications

In the study population, 5,170 (0.3%) deliveries were complicated by chorioamnionitis, 10,832 (0.6%) by intrapartum fever, and 12,923 (0.7%) by neonatal sepsis. The treated group had an increased risk of chorioamnionitis (0.8%, aOR 2.75, 95% CI 2.33–3.23, p < 0.001), intrapartum fever (0.9%, aOR 1.24, 95% CI 1.07–1.44, p = 0.003), and neonatal sepsis (1.3%, aOR 1.55, 95% CI 1.37–1.75, p < 0.001) compared to the reference group (Table 2).

The treated group experienced PTD, pPROM, and infectious complications more frequently than the reference group. For a depiction of the relationship between PTD, pPROM, and infectious complications in the treated and reference groups, see Fig 4.

10.1371/journal.pmed.1003641.g004 Venn diagram illustrating the relationship between preterm delivery (PTD), preterm prelabor rupture of membranes (pPROM), and infectious complications in the treated group and the reference group.

The treated group had PTD, pPROM, and infectious complications more frequently. PTD and deliveries after pPROM were more often complicated by infections in the treated group than in the reference group. The deliveries with infectious complications were more frequently preterm and complicated by pPROM in the treated group than in the reference group.

After stratification for PTD or not, the increased risk of infectious complications in the treated versus the reference group was still statistically significant in the PTD group (chorioamnionitis: aOR 3.96, 95% CI 3.13–5.02, p < 0.001; neonatal sepsis: aOR 1.74, 95% CI 1.43–2.12, p < 0.001), but not in the term delivery group (chorioamnionitis: aOR 1.28, 95% CI 0.98–1.67, p = 0.07; neonatal sepsis: aOR 1.08, 95% CI 0.91–1.29, p = 0.36). There was no clear increase in infectious complications in the HPV infection groups (Table 2).

Stratifying for pPROM in the PTD cases revealed that the aOR for chorioamnionitis was higher in the treated group than in the reference group, in both women with pPROM (aOR 3.68, 95% CI 2.70–5.03, p < 0.001) and women without pPROM (aOR 2.19, 95% CI 1.32–3.61, p = 0.002), but was significantly higher in women with pPROM (p = 0.032). Similarly, the increase in risk of neonatal sepsis in the treated group compared to the reference group was significantly higher in women with PTD with pPROM (aOR 2.70, 95% CI 1.99–3.68, p < 0.001) than in women with PTD without pPROM (aOR 0.86, 95% CI 0.62–1.20, p = 0.39) (p = 0.015 for the interaction).

 Neonatal mortality

There were 2,657 reported cases of neonatal mortality (0.1%). Neonatal mortality was increased in the treated group (aOR 1.79, 95% CI 1.30–2.45, p < 0.001), as well as in the HPV infection (cytology) (aOR 1.81, 95% CI 1.19–2.76, p = 0.006) and HPV infection (HPV test) (aOR 2.69, 95% CI 1.25–5.78, p = 0.011) groups, compared to the reference group (Table 2).

After additional adjustment for PTD, the increased risk of neonatal mortality disappeared in the treated group, suggesting that the risk increase had been mediated by gestational age. However, the risk was still increased in the HPV infection groups, i.e., cytology (aOR 1.64, 95% CI 1.07–2.50, p = 0.024) and HPV test (aOR 2.30, 95% CI 1.06–4.99, p = 0.036).

Of those with neonatal mortality, 4.1% in the reference group and 14.9% in the treated group also contracted chorioamnionitis, and 6.4% in the reference group and 25.5% in the treated group had infants with neonatal sepsis. For an illustration of the relationship between neonatal mortality, infectious complications, and PTD, see Fig 5. The increase in risk of neonatal mortality in the treated group compared to the reference group was significantly higher in women with infectious complications (chorioamnionitis or neonatal sepsis) (aOR 2.06, 95% CI 1.00–4.24, p = 0.049) than in women without infectious complications (aOR 0.90, 95% CI 0.60–1.34, p = 0.59) (p = 0.015 for the interaction).

10.1371/journal.pmed.1003641.g005 Venn diagram illustrating the relationship between preterm delivery (PTD), infectious complications (chorioamnionitis/neonatal sepsis), and neonatal mortality in the treated group and the reference group.

The treated group more frequently had PTD, neonatal mortality, and infectious complications. The deliveries resulting in neonatal mortality more frequently had infectious complications in the treated group than in the reference group.

 Paired analyses

In the paired analyses of 4,680 women with deliveries both before and after treatment, the risk of PTD (aOR 1.26, 95% CI 1.07–1.49, p = 0.007), spontaneous PTD (aOR 1.23, 95% CI 1.02–1.49, p = 0.032), and pPROM (aOR 1.72, 95% CI 1.29–2.29, p < 0.001) were increased after treatment (Table 5). Also, chorioamnionitis and neonatal sepsis had higher odds ratios after treatment (Table 5).

10.1371/journal.pmed.1003641.t005 Obstetric and neonatal outcomes in paired analyses of a woman’s last delivery before treatment and first delivery after treatment—conditional logistic regression analysis (<italic>n =</italic> 4,680 women).
Outcome Before treatment After treatment Unadjusted analyses Adjusted analyses1
n (%) n (%) OR (95% CI) p-Value aOR (95% CI) p-Value
PTD, <37 weeks 288 (6.2) 355 (7.6) 1.23 (1.06–1.44) 0.008 1.26 (1.07–1.49) 0.007
Early PTD, <34 weeks 72 (1.5) 107 (2.3) 1.49 (1.10–2.00) 0.009 1.61 (1–12–2.33) 0.010
Very early PTD, <28 weeks 11 (0.2) 21 (0.4) 1.91 (0.92–3.96) 0.08 4.50 (0.90–22.45) 0.07
Spontaneous PTD 227 (4.9) 278 (5.9) 1.23 (1.03–1.46) 0.023 1.23 (1.02–1.49) 0.032
pPROM 86 (1.8) 155 (3.3) 1.80 (1.39–2.35) <0.001 1.72 (1.29–2.29) <0.001
PROM in deliveries at ≥ 37 weeks 241 (5.5) 246 (5.7) 1.02 (0.85–1.22) 0.85 1.04 (0.85–1.26) 0.74
SGA2 113 (2.4) 71 (1.5) 0.63 (0.47–0.85) 0.002 0.70 (0.50–0.99) 0.043
Apgar score < 7 at 5 minutes 44 (0.9) 63 (1.3) 1.43 (0.97–2.10) 0.068 1.29 (0.82–2.03) 0.28
Neonatal mortality 6 (0.1) 12 (0.3) 2.00 (0.75–5.33) 0.17 —3 —3
Intrauterine fetal death 9 (0.2) 16 (0.3) 1.78 (0.79–4.02) 0.17 —3 —3
Chorioamnionitis 5 (0.1) 36 (0.8) 7.20 (2.83–18.35) <0.001 14.22 (2.09–96.92) 0.007
Intrapartum fever 24 (0.5) 16 (0.3) 0.67 (0.35–1.26) 0.21 0.83 (0.35–1.94) 0.66
Neonatal sepsis 31 (0.7) 43 (0.9) 1.39 (0.87–2.20) 0.17 1.92 (1.02–3.61) 0.044

Statistically significant p-values in bold.

1Adjusted for BMI, marital status, infant’s sex, smoking, and assisted reproduction.

2Missing data about SGA for 7 women before treatment and 4 women after treatment.

3Too few cases to adjust for in multivariable model.

aOR, adjusted odds ratio; CI, confidence interval; HPV, human papillomavirus; OR, odds ratio; pPROM, preterm prelabor rupture of membranes; PROM, prelabor rupture of membranes; PTD, preterm delivery; SGA, small for gestational age.

 HPV infection groups

Except for a higher risk of pPROM (aOR 1.43 95% CI 1.03–1.99, p = 0.034) and PROM (aOR 1.26, 95% CI 1.06–1.50, p = 0.008) in the HPV infection (HPV test) group compared to the HPV infection (cytology) subgroup with no HPV test, no significant differences in outcomes were found between the HPV infection groups (S8 Table).

 Discussion Main findings

In this population-based study, women with HPV infection shortly before or during pregnancy had an increased risk of PTD, spontaneous PTD, pPROM, PROM, and neonatal mortality. An even higher risk of PTD, spontaneous PTD, and pPROM was found in women with previous treatment for CIN. Previous treatment was also associated with PROM, neonatal mortality, and maternal and neonatal infectious complications.

 Comparison with previous studies and interpretation Treatment for CIN and obstetric and neonatal outcomes

The finding that treatment for CIN is associated with infectious pregnancy complications has not been clearly demonstrated before, but an increased risk of chorioamnionitis was suggested by a recent meta-analysis [10]. To the best of our knowledge, this is the first study to demonstrate that it is not only the risk of pPROM but also the risk of PROM at term that is increased after treatment for CIN. Infection is considered to be an important cause of PTD and pPROM [9], while deliveries after pPROM and PROM also entail increased risk of infectious complications [33]. Our results could be explained by an increased risk of ascending bacterial infection in women previously treated for CIN, causing PTD, pPROM, chorioamnionitis, and neonatal sepsis. The finding of an increased risk of PTD, including pPROM, after treatment is consistent with previous studies [10]. The risk increase for PTD was similar to results from birth cohort studies in Finland (1998–2009) and Denmark (1997–2005) [12,14]. The first systematic review that highlighted the risk of PTD after treatment for CIN was published in 2006 [34]. In our study, 40% of women treated for CIN were treated after 2006. Eighty-nine percent were treated after 1996, indicating that the majority had been treated with the LLETZ technique. The results of this study thus reflect the risks related to current treatment methods.

 HPV infection and obstetric and neonatal outcomes

In this study, women with HPV infection had increased risk of PTD, pPROM, PROM, and neonatal mortality. Previous studies have presented conflicting results. A recent population-based study did not confirm an increased risk of PTD in women positive for high-risk HPV without CIN2+ (aOR 1.11, 95% CI 0.75–1.66) [20], perhaps due to a lack of power based on the much smaller sample. The risk estimates in our study (aOR 1.21 for cytology and aOR 1.19 for HPV test) were slightly lower than that suggested by a recent meta-analysis (aOR 1.50), but within the 95% CI of that study (1.19–1.88) [22]. HPV has been found in the placenta [19,35], and it has been hypothesized that HPV might cause placental dysfunction, leading to PTD [18,19]. However, in this study we found no increase in SGA in the exposed women, suggesting a mechanism other than dysfunctional placenta. In a mouse model, viral infection of the cervix during pregnancy reduced the capacity of the female reproductive tract to prevent ascending bacterial infection [36]. We did not confirm any association between HPV infection and clinical infectious complications. However, infections associated with PTD are known to be subclinical to a major extent [37].

It is still unclear whether the HPV infection itself, common confounders, or a genetic predisposition is the causal link behind the association between CIN and PTD. However, our results suggest that HPV infection might be an important factor. Women developing CIN2+ after delivery also had a small increased risk of PTD and spontaneous PTD, although it was not significant in the subgroup of women who were diagnosed more than 3 years after delivery. This may possibly reflect an ongoing HPV infection during pregnancy and delivery in women with earlier diagnosis of CIN2+ after birth. These findings contradict the hypothesis of a common genetic susceptibility to both persistent HPV infection and PTD or an association merely due to confounding.

 Strengths and limitations

To the best of our knowledge, this is the largest study to date examining the associations of HPV infection shortly before or during pregnancy and treatment for CIN with obstetric and neonatal outcomes. It comprises an entire population, and we believe it compares the largest number of deliveries before and after treatment for CIN in the same women published so far.

As this is an observational study, causality cannot be established and residual confounding cannot be ruled out despite thorough adjustments. However, the risk increases for PTD, spontaneous PTD, pPROM, and chorioamnionitis found in the treated group were supported by similar findings in the paired analyses, in which 2 deliveries in the same woman were compared.

The definition of HPV infection in this study has some potential limitations. To begin with, relying on positive screening tests may lead to an underestimation of the true incidence and prevalence as many infections can occur and resolve between testing. A small minority of HPV tests might have been positive due to exclusive detection of low-risk strains, although the tests used at Swedish laboratories predominantly specifically detect high-risk HPV. Since HPV test results only became available in 2007, abnormal cytology was used as a proxy for HPV infection, as in earlier studies [21,38]. A Swedish study found that 72% of women aged under 40 years with low-grade abnormal cytology were positive for high-risk HPV [39]. Since the abnormal cytology group in this study also included high-grade abnormality, abnormal cytology can be assumed to represent the presence of high-risk HPV to a high degree. Positive HPV tests/cytology up to 6 months before conception were included in the HPV infection groups, and some infections might have resolved before pregnancy. However, such misclassification would have attenuated a true effect. We did not require a negative HPV test in the reference group, and some women might have had an undetected HPV infection. However, such misclassification would have attenuated the associations found for the exposure groups compared to the reference group. Since no national treatment data are available, CIN3 was used as a proxy for treatment; all women treated for high-grade lesions are thus not included in the treated group. For the paired analyses it was not possible to adjust for maternal age and parity, and these results must thus be interpreted with caution.

 Implications and next step for research

The use of HPV tests in cervical cancer screening has increased during the last decade, which will facilitate large population-based analysis of the relationship of HPV infection and pregnancy outcomes in the near future. Our results support general HPV vaccination programs, and future studies in vaccinated cohorts will ascertain whether PTD and neonatal mortality decrease. Additional experimental studies are also needed to establish the causal pathways linking HPV infection and treatment for CIN to PTD and other adverse obstetric outcomes. This may be a key to understanding the biological mechanism leading to PTD. We suggest that pregnancies after treatment for CIN should be regarded as high-risk pregnancies.

 Conclusion

This large population-based study demonstrates that women with HPV infection shortly before or during pregnancy have an increased risk of PTD, pPROM, PROM, and neonatal mortality. Treatment for CIN was associated with further increased risk of PTD and pPROM and was also associated with PROM, neonatal mortality, and an increased risk of maternal and neonatal infectious complications. These results suggest that pregnancies after treatment for CIN should be regarded as high-risk pregnancies and counseled accordingly. Furthermore, our results support general HPV vaccination programs.

 Supporting information <p>(DOC)</p> </caption> </supplementary-material> <supplementary-material id="pmed.1003641.s002" mimetype="application/msword" position="float" xlink:href="info:doi/10.1371/journal.pmed.1003641.s002" xlink:type="simple"> <label>S1 Table</label> <caption> <title>Diagnosis codes, according to the International Classification of Diseases–10th Revision (ICD-10), registered in the Swedish Medical Birth Register, leading to exclusion.

(DOC)

 Definition of study groups.

(DOC)

 Classification of cervical cytology and histology.

(DOC)

 Outcome definition based on diagnosis codes according to the International Classification of Diseases–10th Revision (ICD-10) in the Swedish Medical Birth Register.

(DOC)

 Obstetric and neonatal outcomes in exposure groups compared to the reference group—univariable logistic regression analyses.

(DOC)

 Obstetric and neonatal outcomes in the subsequent CIN2+ group compared with the reference group, stratified by interval from delivery to CIN2+ diagnosis—univariable logistic regression analyses.

(DOC)

 Obstetric and neonatal outcomes in the treated group compared to the HPV infection groups and the subsequent CIN2+group—univariable logistic regression analyses.

(DOC)

 Outcomes in the HPV infection (cytology) group compared to the HPV infection (HPV test) group—univariable and multivariable logistic regression analyses, deliveries 2007–2016.

(DOC)

 Abbreviations aOR

adjusted odds ratio

 CIN

cervical intraepithelial neoplasia

 HPV

human papillomavirus

 LLETZ

large loop excision of the transformation zone

 MBR

Swedish Medical Birth Register

 NKCx

Swedish National Cervical Screening Registry

 pPROM

preterm prelabor rupture of membranes

 PROM

prelabor rupture of membranes

 PTD

preterm delivery

 SGA

small for gestational age

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 10.1371/journal.pmed.1003641.r002 Decision Letter 1 Moyer Caitlin Senior Editor 2021 Caitlin Moyer This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Submission Version 1

16 Feb 2021

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We ask every co-author listed on the manuscript to fill in a contributing author statement, making sure to declare all competing interests. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. If new competing interests are declared later in the revision process, this may also hold up the submission. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT. You can see our competing interests policy here: http://journals.plos.org/plosmedicine/s/competing-interests.

Please use the following link to submit the revised manuscript:

https://www.editorialmanager.com/pmedicine/

Your article can be found in the "Submissions Needing Revision" folder.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see http://journals.plos.org/plosmedicine/s/submission-guidelines#loc-methods.

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

We look forward to receiving your revised manuscript.

Sincerely,

Caitlin Moyer, Ph.D.

Associate Editor

PLOS Medicine

plosmedicine.org

-----------------------------------------------------------

Requests from the editors:

1.Title: Please revise your title according to PLOS Medicine's style. Your title must be nondeclarative and not a question. It should begin with main concept if possible. "Effect of" should be used only if causality can be inferred, i.e., for an RCT. Please place the study design ("A randomized controlled trial," "A retrospective study," "A modelling study," etc.) in the subtitle (ie, after a colon). We suggest: “Associations of reated and untreated human papillomavirus infection with preterm delivery and neonatal mortality: A Swedish population-based study” or similar.

2. Abstract: Methods and Findings: Please provide some of the key summary demographics of the population.

3. Abstract: Methods and Findings: Please quantify the main results (with both 95% CIs and p values).

4. Abstract: Methods and Findings: In the last sentence of the Abstract Methods and Findings section, please describe the main limitation(s) of the study's methodology.

5. Abstract: Conclusions: Please address the study implications without overreaching what can be concluded from the data; the phrase "In this study, we observed ..." may be useful.

6 .Abstract: Conclusions: Please avoid language implying causality (“Treatment for CIN increases risks ruther and seems to confer a risk…”)

7. Author summary: At this stage, we ask that you include a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract. Please see our author guidelines for more information: https://journals.plos.org/plosmedicine/s/revising-your-manuscript#loc-author-summary

8. Main text: Throughout: Please do not include spaces within brackets of in-text citation (e.g. [2,3]) and please place the brackets before the punctuation (e.g. Page 4, line 2).

9. Introduction: Please do conclude the Introduction by mentioning your study objective/hypothesis, but this does not need to be in a separate “Objectives” section within the introduction.

10. Methods/ figure 1: Is it possible to give additional clarification/explanation of the 600,000+ excluded women (did not fulfil criteria of any group) from Fig 1 flow chart (reasons for exclusion)?

11. Methods: Please add the following statement, or similar, to the Methods: "This study is reported as per the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline (S1 Checklist)."

12. Methods: Did your study have a prospective protocol or analysis plan? Please state this (either way) early in the Methods section.

a) If a prospective analysis plan (from your funding proposal, IRB or other ethics committee submission, study protocol, or other planning document written before analyzing the data) was used in designing the study, please include the relevant prospectively written document with your revised manuscript as a Supporting Information file to be published alongside your study, and cite it in the Methods section. A legend for this file should be included at the end of your manuscript.

b) If no such document exists, please make sure that the Methods section transparently describes when analyses were planned, and when/why any data-driven changes to analyses took place.

c) In either case, changes in the analysis-- including those made in response to peer review comments-- should be identified as such in the Methods section of the paper, with rationale.

13. Results: Please provide more quantitative description of the background differences in study groups (age, parity, smoking).

14. Results: For all results presented in the text, please provide both the 95% CIs and p values.

15. Results: “Small for gestational age and Apgar score” section: please clarify which groups are meant by “The groups did not differ…” in the second sentence of this paragraph.

16. Results: “HPV infection groups” section: please report the result for this association “Except for a higher risk of pPROM and PROM in the HPV infection (HPV test) group” and specify the comparison group.

17. Discussion: Please present and organize the Discussion as follows: a short, clear summary of the article's findings; what the study adds to existing research and where and why the results may differ from previous research; strengths and limitations of the study; implications and next steps for research, clinical practice, and/or public policy; one-paragraph conclusion.

18. References: Please double check the formatting (such as use of italics- e.g. BMJ format in ref 8 and 15). Please provide an English translation for ref 26, 28, 29, 30.

19. Table 2, Table 3, Table, 4, and Table 5: Please present actual p values rather than representing with asterisks. Please provide the unadjusted results in addition to the adjusted analyses (these may be in a supporting information table, if desired).

20. Figures 2 and 3: Please include the p values with the arrows, if possible. As mentioned for the Tables, the unadjusted analyses should be included, whether in the main text or supporting information.

21. S5 Table: Please provide p values for each comparison, rather than indicating p values with asterisks. Please provide the unadjusted analyses.

22. STROBE checklist: Thank you for including the checklist. It would be appropriate to refer to locations in the text for each item with an additional column on the right-hand side of the table- When completing the checklist, please use section and paragraph numbers, rather than page numbers.

Comments from the reviewers:

Reviewer #1: This retrospective population-based register study of women with singleton deliveries registered in the Swedish Medical Birth Register 1999-2016, aims to investigate whether HPV infection in conjunction with pregnancy, as well as previous treatment for CIN, is associated with an increased risk of PTD and other adverse obstetric and neonatal outcomes.

Comments:

There are some typos in the text that need rectifying.

The STROBE checklist is suitably included in the supplementary material.

Descriptive data are appropriately presented, and the comparison of exposure groups by logistic regression (adjusted for socioeconomic and health-related confounders) is a technically valid and robust approach.

Are there other factors that may be associated with PTD that can be included as potential confounders within the models? Alcohol or drug abuse, for instance?

Table 1 is very informative. Did the authors complete any statistical testing to explore if differences between groups are significant or not?

Table 2 is an efficient and effective way to communicate the main results.

Perhaps more caution should be applied when drawing inferences from the paired analysis. These results might not be generalisable due to the specific nature of the cohort analysed.

For instance: Might multiple births be affecting the outcomes? Or, the effect of having treatment after at least one prior delivery? Are there other potential intra-woman confounders in this analysis (e.g age at delivery older after treatment, although it is noted that maternal age is included as a covariate in the model)?

The main limitations have been acknowledged, including the fact that this in an observational study (and therefore, causality cannot be inferred), the potential for confounding, and the possibility of misclassification.

Overall, this is a thorough study looking at different subgroups and their outcomes over a large cohort and incorporating a good use of visualisation in the figures which helps to clearly communicate the research findings.

Reviewer #2: This is a large population-based study that investigates in detail the association between HPV infection, CIN or CIN treatment and PTB. The authors have put a lot of effort and have conducted a comprehensive analysis by including all possible comparison groups (women with positive HPV testing prior to delivery; women with abnormal cytology prior to delivery; women treated for CIN3 prior to delivery; women with CIN2+ after delivery; women with no history of HPV/CIN prior to delivery) and performing all possible comparison combinations including self-matching. The authors very nicely associate their findings with previous studies, and suggest potential mechanism of PTB based on their findings. Although the main findings of this study have been suggested by other studies, findings were conflicting or not conclusive before as the authors describe in the manuscript. This is the largest and most comprehensive study so far trying to cast light on the long-standing debate whether HPV infection per se increases the risk of PTB, and therefore I highly recommend it for publication in PLoS Medicine.

I have only some minor comments to the authors:

-Line 34: Replace "outcome" with "outcomes"

-In the HPV infection group, I do not understand what the authors mean by "between six months prior to conception and delivery". I think that they mean "within six months prior to conception or during pregnancy".I suggest rephrasing throughout the text.

-Additionally, in abstract the various comparison groups are not very clear. I understand that there is a word limitation, but if possible, authors could describe the different groups in more details, especially the timing of the abnormal test/intervention. By reading the abstract only, it is not very clear for example whether the HPV positivity group includes women with HPV prior to pregnancy, during pregnancy, or both.

-Page 7, lines 16-17: I suggest adding citations for the statistical software that the authors have used.

-Page 7, line 32: Replace "Subsequent" with "subsequent"

Reviewer #3: This is a well-written substantive retrospective paper based on over 1 million births in Sweden.

1. p.5 Line 29. Women with exclusively normal cytology. Does that mean that they had documented negative HPV tests? I ask because if they did not, how do you know that they were not also HPV positive which would put them in the comparison group. When the term Lifetime is used -what does that mean? Is it the time prior to delivery?

2. p.6, line 13: It is possible that women who have CIN2+ at a young age can clear spontaneously. Did you exclude because they got categorized into the other exposure groups?

3. How did you account for parity? Were women who had multiple births counted as one person or was each birth counted? This could mean a women with multiple preterm births could be counted multiple times with the same characteristics over and over again.

4. P2, line 31: With the high prevalence of HPV infection in anyone who has ever been sexually active, it may be more appropriate to say, "Women with detectable HPV infection..."

Any attachments provided with reviews can be seen via the following link:

[LINK]

 10.1371/journal.pmed.1003641.r003 Author response to Decision Letter 1 Submission Version 2

5 Mar 2021

Submitted filename: Response to reviewers.doc

 10.1371/journal.pmed.1003641.r004 Decision Letter 2 Moyer Caitlin Senior Editor 2021 Caitlin Moyer This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Submission Version 2

19 Apr 2021

Dear Dr. Wiik,

Thank you very much for re-submitting your manuscript "Associations of treated and untreated human papillomavirus infection with preterm delivery and neonatal mortality: A Swedish population-based study" (PMEDICINE-D-20-06245R2) for review by PLOS Medicine.

I have discussed the paper with my colleagues and the academic editor. I am pleased to say that provided the remaining editorial and production issues are dealt with we are planning to accept the paper for publication in the journal.

The remaining issues that need to be addressed are listed at the end of this email. Please take these into account before resubmitting your manuscript:

[LINK]

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

In revising the manuscript for further consideration here, please ensure you address the specific points made by the editors. In your rebuttal letter you should indicate your response to the editors' comments and the changes you have made in the manuscript. Please submit a clean version of the paper as the main article file. A version with changes marked must also be uploaded as a marked up manuscript file.

Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. If you haven't already, we ask that you provide a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract.

We expect to receive your revised manuscript within 1 week. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

We ask every co-author listed on the manuscript to fill in a contributing author statement. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT.

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript.

Please note, when your manuscript is accepted, an uncorrected proof of your manuscript will be published online ahead of the final version, unless you've already opted out via the online submission form. If, for any reason, you do not want an earlier version of your manuscript published online or are unsure if you have already indicated as such, please let the journal staff know immediately at plosmedicine@plos.org.

If you have any questions in the meantime, please contact me or the journal staff on plosmedicine@plos.org.  

We look forward to receiving the revised manuscript by Apr 26 2021 11:59PM.   

Sincerely,

Caitlin Moyer, Ph.D.

Associate Editor 

PLOS Medicine

plosmedicine.org

------------------------------------------------------------

Requests from Editors:

1. Abstract: Methods and Findings: Please clarify if the OR reported in the text here are the adjusted ORs.

2. Abstract: Methods and Findings: Page 3, Line 1-2: We suggest revising the limitations sentence as “Limitations of the study include the retrospective design and the fact that because HPV test results only became available in 2007, abnormal cytology was used as a proxy for HPV infection.”

3. Author summary: What did the researchers do and find? In the first bullet point of this section, we suggest removing “...is, so far, the largest published and the first to demonstrate…”

4. Author summary: What do these findings mean? We suggest providing some clarification on the final bullet point in this section, for example “These results support the idea that strategies to mitigate HPV infection, such as vaccination programs, may be beneficial for maternal and neonatal pregnancy outcomes.” or similar.

5. Methods: Page 6: Lines 6-8: Please clarify this sentence to: “We did not publish the analysis plan but the overall exposure, outcomes, confounders and analyses were planned in 2015 by the research team based on hypotheses drawn from previous studies.”

6. Methods: Page 6, line 19: Please change to “30.2 years”

7. Results: Page 17, line 4: We suggest replacing “non-significant” with “not statistically significant” or similar.

8. Discussion: Page 21: Lines 25-26: We suggest revising to: “However, our results suggest that HPV infection might be an important factor.”

9. Discussion: Page 22: Line 1-2: Please revise to: “To the best of our knowledge, this is the largest study to date examining the associations of HPV infection in conjunction with pregnancy and treatment for CIN with obstetric and neonatal outcomes.” Please also temper the second sentence (compares the largest number…) at lines 3-4 with “to the best of our knowledge” or similar.

10. Discussion: Page 22, Line 11: We suggest changing “...implies an obvious underestimation…” to “...may lead to an underestimation of the true incidence…” or similar.

11. Discussion: Page 22, Line 27-28: Please revise to “For the paired analyses it was not possible to adjust for maternal age and parity and these results must thus be interpreted with caution.”

12. Discussion: conclusions: Page 23: Line 9-11: Please revise to avoid causal implications: “Treatment for CIN was associated with further increased risk of PTD, pPROM, PROM and neonatal mortality and was associated with increased risk of maternal and neonatal infectious complications. These results suggest it may be beneficial to regard pregnancy after treatment for CIN as high-risk pregnancies and counselled accordingly.”

13. References: Please check journal name abbreviations (Ref 2 should be J Natl Cancer Inst, Ref 3 should be Eur J Cancer). Please remove the italics from ref 17, and 27. Please use the "Vancouver" style for reference formatting, and see our website for other reference guidelines https://journals.plos.org/plosmedicine/s/submission-guidelines#loc-references

14. Figure 2. Please give an overall title for Figure 2, noting the differences between panels a and b.

15. Figure 4 and Figure 5. Please provide the numbers in addition to percentages.

16. Table 5: Please note that the line numbers are overlapping with the right-side column for the last 5 rows.

17. Supporting information: If possible, please include each item as a separate file.

18. S8 Table: It is not clear what part of the table this reference is supporting (1. M. HWW. In: Wagner M MA, Aryel R. , editor. Handbook of Biosurveillance Elsevier 2006. p. 439-52.)

Any attachments provided with reviews can be seen via the following link:

[LINK]

 10.1371/journal.pmed.1003641.r005 Author response to Decision Letter 2 Submission Version 3

24 Apr 2021

Submitted filename: Rebuttal letter .doc

 10.1371/journal.pmed.1003641.r006 Decision Letter 3 Moyer Caitlin Senior Editor 2021 Caitlin Moyer This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Submission Version 3

29 Apr 2021

Dear Dr Wiik, 

On behalf of my colleagues and the Academic Editor, Jenny E Myers, I am pleased to inform you that we have agreed to publish your manuscript "Associations of treated and untreated human papillomavirus infection with preterm delivery and neonatal mortality: A Swedish population-based study" (PMEDICINE-D-20-06245R3) in PLOS Medicine.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. Please be aware that it may take several days for you to receive this email; during this time no action is required by you. Once you have received these formatting requests, please note that your manuscript will not be scheduled for publication until you have made the required changes.

In the meantime, please log into Editorial Manager at http://www.editorialmanager.com/pmedicine/, click the "Update My Information" link at the top of the page, and update your user information to ensure an efficient production process. 

PRESS

We frequently collaborate with press offices. If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximise its impact. If the press office is planning to promote your findings, we would be grateful if they could coordinate with medicinepress@plos.org. If you have not yet opted out of the early version process, we ask that you notify us immediately of any press plans so that we may do so on your behalf.

We also ask that you take this opportunity to read our Embargo Policy regarding the discussion, promotion and media coverage of work that is yet to be published by PLOS. As your manuscript is not yet published, it is bound by the conditions of our Embargo Policy. Please be aware that this policy is in place both to ensure that any press coverage of your article is fully substantiated and to provide a direct link between such coverage and the published work. For full details of our Embargo Policy, please visit http://www.plos.org/about/media-inquiries/embargo-policy/.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

Thank you again for submitting to PLOS Medicine. We look forward to publishing your paper. 

Sincerely, 

Caitlin Moyer, Ph.D. 

Associate Editor 

PLOS Medicine