- Design
- Nationwide population-based matched case-control study
- Population
- 624,713 singleton births to nulliparous women aged 16-35, Sweden 2006-2023
- Primary outcome
- Preterm birth and spontaneous preterm birth
- Effect
- Preterm birth aOR 0.95 (95% CI 0.91-0.99)
A Swedish nationwide matched case-control study examined 624,713 first singleton births to women aged 16 to 35 between 2006 and 2023, of whom about 15% had received quadrivalent human papillomavirus (HPV) vaccine before pregnancy. Published in The BMJ on 7 October 2026.
After adjustment, prior vaccination was associated with slightly lower odds of preterm birth (adjusted OR 0.95, 95% CI 0.91 to 0.99), very preterm birth (0.85) and severely small-for-gestational-age infants (0.92). Associations were stronger in women vaccinated younger.
The effects are small and observational. Vaccinated women may differ in ways adjustment cannot fully capture. One plausible mechanism is fewer cervical treatments for precancer, which themselves raise preterm risk.
The main value is reassurance: in a very large population, there was no sign of harm to later pregnancies.
- Reassure young women that HPV vaccination showed no signal of harm to later pregnancies
- Use the opportunity to check HPV vaccination status in girls and young women
- Do not present lower preterm birth as an established benefit of vaccination
Why it matters
It answers a common worry from parents and young women about vaccination and future pregnancy.
Don't overread it
This was observational, and the differences were small; it cannot show the vaccine prevents preterm birth.
The statistics, in plain English
An odds ratio of 0.95 means about 5% lower odds, and the upper limit of 0.99 is close to no effect. With over 600,000 births, even tiny differences reach statistical significance without being clinically important.
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