A national case-control study from Sweden, published in The BMJ, found that women vaccinated against human papillomavirus (HPV) had significantly lower risks of several adverse pregnancy outcomes. Analyzing nearly 625,000 singleton births among nulliparous women ages 16 to 35, researchers reported reduced odds of preterm birth (adjusted odds ratio 0.95), very preterm birth (0.85), and spontaneous preterm birth (0.95) for those who had received a quadrivalent HPV shot compared with unvaccinated women.
The link was stronger for women vaccinated before age 17, with adjusted odds ratios of 0.90 for preterm birth and 0.89 for spontaneous preterm birth. The authors noted that earlier vaccination may provide longer protection before reproductive years and could reduce HPV exposure before sexual debut. They also suggested that HPV might interfere with embryonic development or that preventing high-grade cervical lesions—and the treatments for them—could lower preterm birth risk.
However, the associations weakened when researchers adjusted for high-grade cervical lesions before childbirth, and the study lacked detailed cervical treatment datacars, so the authors called the mechanistic analysis exploratory. No significant differences were seen for PROM, stillbirth, or neonatal mortality overall, though women vaccinated before 17 had lower odds of preterm PROM and severe small-for-gestational-age infants. The researchers emphasized that while individual-level differences were modest, they could translate into meaningful population-level public health benefits. Limitations included possible residual confounding from sexual behavior and catch-up vaccination, especially among women vaccinated at 17 or older.