- Design
- Nationwide matched case-control study
- Population
- 624,713 singleton first births in Sweden, 2006–2023
- Primary outcome
- Preterm birth (<37 weeks) and spontaneous preterm birth
- Effect
- Preterm birth adjusted OR 0.95 (95% CI 0.91–0.99)
Using Swedish national registers from 2006 to 2023, investigators matched 624,713 singleton first births to women aged 16 to 35 and compared quadrivalent HPV vaccination before pregnancy across adverse outcomes. About 15% of the mothers had been vaccinated.
After adjustment, vaccination was associated with slightly lower odds of preterm birth (adjusted OR 0.95), very preterm birth (0.85) and severely small-for-gestational-age infants (0.92). The associations were stronger in women vaccinated younger. No outcome was worse in vaccinated women.
One plausible pathway is fewer cervical precancers and therefore fewer excisional procedures, which are known to raise preterm risk. But vaccinated and unvaccinated women differ in many ways that registers capture imperfectly, and the effects are small.
The practical value is reassurance: a large population study found no signal of harm to later pregnancies. That is a useful answer for a hesitant parent or young woman.
- Reassure patients that a large Swedish study found no increase in adverse pregnancy outcomes after prior HPV vaccination.
- Recommend HPV vaccination on its cancer-prevention merits; any pregnancy benefit is secondary and unproven.
- Vaccinate at the recommended younger ages, when protection is greatest.
- Check vaccination status when counselling young women about future pregnancy and cervical screening.
Why it matters
It answers a common worry about HPV vaccination with real-world data at national scale.
Don't overread it
This was observational; it cannot show that vaccination prevents preterm birth.
The statistics, in plain English
An adjusted odds ratio of 0.95 means about 5% lower odds, and the upper confidence limit of 0.99 sits just below 1, so the effect is small and close to no difference. Case-control designs can adjust only for what the registers record, so health-conscious behaviour may explain part of it.
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