- Design
- Nationwide population-based 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 aOR 0.95 (0.91–0.99); very preterm aOR 0.85 (0.75–0.97)
A nationwide Swedish case-control study in The BMJ (7 October) linked 624,713 first singleton births between 2006 and 2023 to vaccination records. About 15% of mothers had received quadrivalent HPV vaccine before pregnancy.
Vaccination was associated with slightly lower odds of preterm birth (adjusted odds ratio 0.95), very preterm birth (0.85) and severely small babies (0.92). Associations were stronger in women vaccinated younger.
A plausible route is fewer cervical lesions and so fewer excisional procedures, which raise preterm risk. But vaccinated women may differ in ways that adjustment cannot capture. The practical value is reassurance and one more reason to complete vaccination, not a new claim to make to parents.
- Vaccination before pregnancy was linked to slightly fewer preterm births
- Effects were larger in women vaccinated at younger ages
- Useful reassurance for parents worried about later fertility or pregnancy
- Offer catch-up vaccination where eligible, under local schedules
Why it matters
Concern about future pregnancy is a common reason parents delay HPV vaccination, and this points the other way.
Don't overread it
Observational — residual confounding may explain part of the small association.
The statistics, in plain English
An odds ratio of 0.95 (95% CI 0.91 to 0.99) is a small effect whose upper limit almost touches 1. In a study this large, even tiny differences reach significance, so the size of the effect matters more than the P value.
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