HPV Vaccination Linked to Lower Risk of Preterm Birth: Swedish Study
Sweden: A national case-control study from Sweden found that women vaccinated against human papillomavirus (HPV) had significantly lower risks of preterm, very preterm, and spontaneous preterm birth. The protective associations were stronger among women vaccinated before age 17. However, adjustment for high-grade cervical lesions before childbirth weakened these associations, suggesting that cervical lesions may partly explain the observed relationship.
Published in The BMJ, the study was conducted by Zhongsong Zhang, Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, and colleagues. The researchers investigated whether quadrivalent HPV (qHPV) vaccination received before pregnancy was associated with subsequent pregnancy outcomes.
HPV vaccination is primarily used to prevent HPV-related cancers. However, previous evidence has linked HPV infections and the treatment of cervical lesions with an increased risk of adverse pregnancy outcomes. Earlier studies examining whether vaccination could reduce these risks were limited by a lack of nationwide data and adequate adjustment for confounding factors.
For the study, researchers analysed 624,713 singleton births among nulliparous women aged 16–35 years in Sweden between 2006 and 2023. Of these, 92,620 women (14.8%) had received qHPV vaccination before pregnancy. Using a nationwide, population-based matched case-control design, the team assessed preterm birth before 37 weeks, its subtypes, and spontaneous preterm birth as primary outcomes. Other outcomes included premature rupture of membranes, small-for-gestational-age infants, stillbirth, and neonatal mortality. Cases and controls were matched for maternal age at birth and calendar year of conception.
The analysis revealed the following findings:
- Preterm birth: Vaccination was associated with 5% lower adjusted odds of birth before 37 weeks (adjusted odds ratio [aOR] 0.95).
- Very preterm birth: The adjusted odds were 15% lower for births between 28 and 31 weeks (aOR 0.85).
- Spontaneous preterm birth: Vaccinated women had 5% lower adjusted odds (aOR 0.95).
- Other pregnancy outcomes: Vaccination was associated with lower odds of preterm prelabour rupture of membranes (aOR 0.93) and severe small-for-gestational-age birth, defined as birth weight below the third centile (aOR 0.92).
- Age at vaccination: Risk reductions were generally more pronounced among women vaccinated at younger ages.
The study’s observational design limits causal conclusions, and residual confounding from vaccination uptake, HPV exposure, health-seeking behaviour and reproductive factors cannot be ruled out. Lack of data on post-vaccination HPV infections and cervical treatments also limited assessment of underlying mechanisms. Rare outcomes, including stillbirth and neonatal mortality, had limited statistical power.
The findings suggest that HPV vaccination may reduce certain adverse pregnancy outcomes beyond its established cancer-prevention benefits. The researchers emphasised timely school-based vaccination and recommended including potential reproductive benefits in future policy and cost-effectiveness evaluations.
Reference:
BMJ 2026;395:e100739
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