HPV vaccination before pregnancy linked to slightly fewer preterm births

Design

Nationwide population-based matched case-control study

Population

624,713 singleton first births in Sweden, 2006-2023

Primary outcome

Preterm birth and spontaneous preterm birth

Effect

Preterm birth adjusted OR 0.95 (95% CI 0.91 to 0.99); very preterm 0.85 (0.75 to 0.97)

A nationwide Swedish matched case-control study examined 624,713 singleton first births to women aged 16 to 35 between 2006 and 2023; 14.8% of the mothers had received quadrivalent HPV vaccine before pregnancy.

After adjustment, vaccination was associated with lower odds of every adverse outcome studied. The significant ones were preterm birth (adjusted OR 0.95, 95% CI 0.91 to 0.99), very preterm birth at 28 to 31 weeks (0.85), spontaneous preterm birth (0.95) and severely small-for-gestational-age infants (0.92). The associations were stronger in women vaccinated younger.

A plausible link exists: HPV-related cervical disease and its treatment, such as excisional procedures, are known to raise preterm birth risk. But women who are vaccinated may differ in ways that adjustment does not fully capture. The practical point is reassurance, not a new indication: the vaccine is not associated with harm in later pregnancy, and the case for vaccinating early is strengthened.

• HPV vaccination before pregnancy was not associated with any adverse pregnancy outcome in over 600,000 births.
• The association with fewer preterm births was small and stronger with vaccination at younger ages.
• Use this to reassure parents and young women who ask whether vaccination affects later pregnancy.
• The study used the quadrivalent vaccine; whether other HPV vaccines show the same pattern was not examined.

Why it matters

Pregnancy safety is a frequent question from parents weighing HPV vaccination for their daughters.

Don't overread it

This is observational; it shows an association with fewer preterm births, not that the vaccine prevents them.

The statistics, in plain English

An odds ratio of 0.95 means about 5% lower odds, a small difference that only shows up as significant because the study is very large. The upper limit of 0.99 sits close to 1, so the true effect could be close to nothing. Residual confounding, unmeasured differences between vaccinated and unvaccinated women, could explain an effect this size.

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