BMJ Study: HPV Vaccination Before Pregnancy Linked to Lower Preterm Birth Risk

Women who received the quadrivalent human papillomavirus (HPV) vaccine prior to their first pregnancy show a reduction in the risk of preterm birth and specific pregnancy complications. A large-scale population-based study published in The BMJ indicates that vaccination is linked to lower rates of early delivery and fetal growth restriction.

Clinical Insights for Expectant Mothers

• Reduced Preterm Risk: Vaccination is associated with a 5% lower risk of overall preterm birth and a 15% reduction in very preterm births (28–31 weeks gestation).
• Preventative Mechanisms: The vaccine appears to mitigate risks by preventing HPV infection and subsequent cervical lesions that could otherwise necessitate procedures.
• Age-Dependent Efficacy: Women vaccinated before age 17 demonstrated more distinct health outcomes, including a 10% lower risk of preterm birth compared to non-vaccinated cohorts.

The study, published in The BMJ, compared women who received the quadrivalent HPV vaccine—which targets four HPV types, including types 16 and 18—against those who remained unvaccinated. By matching participants based on maternal age and calendar year of pregnancy, and adjusting for variables including body mass index (BMI), smoking status, diseases, use of assisted reproductive technology, and income and education levels, the investigators isolated the potential impact of the vaccine on obstetric outcomes.

The findings revealed that among the vaccinated women (14.8% of the cohort), the adjusted odds ratio (aOR) for preterm birth was 0.95, representing a 5% decrease in risk. The protective association was even more pronounced regarding specific complications: vaccinated women showed a 7% lower risk of premature rupture of membranes and an 8% lower risk of delivering a small-for-gestational-age infant.

Evidence-Based Mechanisms for Reduced Obstetric Risk

While the study was observational, researchers suggest that the reduction in adverse pregnancy outcomes is likely tied to the vaccine’s primary function: preventing HPV infection. HPV infection is a primary cause of cervical cancer and has also been linked in research to an increased risk of preterm birth and some pregnancy complications. By preventing these infections, the vaccine may also reduce the necessity for procedures to treat cervical lesions, which may lower the risk of preterm birth.

Outcome Measure	Adjusted Risk Reduction (All Vaccinated)	Adjusted Risk Reduction (Vaccinated <17)
Preterm Birth (<37 weeks)	5%	10%
Very Preterm Birth (28–31 weeks)	15%	Not explicitly stated
Premature Membrane Rupture	7%	14%
Small for Gestational Age	8%	9%

HPV Vaccine Is Safe for Pregnancy Outcomes

The HPV vaccine is considered safe in terms of pregnancy outcomes and is part of global strategies and routine immunization programs.

Global Public Health Implications

This research provides further evidence for the utility of routine vaccination programs as a strategy for broader reproductive health. The study authors emphasized that while these results do not establish a direct causal link, they suggest that the benefits of HPV vaccination—beyond cancer prevention—include reducing the risk of negative pregnancy outcomes. This data supports the continued prioritization of national immunization programs. The research was supported by registry data from the Swedish healthcare system, reinforcing the value of large-scale, population-based longitudinal studies in informing clinical practice and public health policy.

References

• Zhang, Z., et al. (2026). “Quadrivalent human papillomavirus vaccination before pregnancy and pregnancy outcomes: nationwide, population based case-control study.” The BMJ.