Women vaccinated against human papillomavirus before pregnancy show a 15 percent lower risk of very preterm birth, according to nationwide Swedish registry data published in The BMJ. The findings suggest immunization benefits extend past cancer prevention into improved reproductive outcomes.
Medical expectations for human papillomavirus vaccination center on cancer prevention, but new data shows the shot may also protect pregnancies. A nationwide study tracking more than 624,000 first-time births in Sweden establishes a link between vaccination prior to conception and reduced rates of major pregnancy complications as reported by CIDRAP.
Published on October 7, 2026, the observational research analyzed birth records from 2006 through 2023 for mothers aged 16 to 35. Of the 624,713 singleton births evaluated, exactly 92,620 mothers—14.8 percent of the cohort—had received at least one dose of the quadrivalent vaccine before conceiving.
Vaccinated women experienced lower odds across multiple adverse pregnancy endpoints after researchers adjusted for maternal age at childbirth, body mass index, smoking, and assisted reproduction according to Medical Daily.
Vaccinated Mothers Face Lower Preterm Birth Rates
The risk reduction grew more pronounced for earlier deliveries. Vaccinated women showed a 15 percent lower odds of very preterm birth, which occurs between the 28th and 31st weeks of gestation noted Medical Daily. This is a critical window when newborns frequently require weeks of intensive neonatal care.
The study also found a five percent overall reduction in the odds of any preterm birth—defined as delivery before 37 weeks—among vaccinated mothers.
Vaccinated participants demonstrated lower odds of spontaneous preterm labor, preterm prelabor rupture of membranes, and delivering an infant severely undersized for gestational age according to Inside Precision Medicine.
“the benefits of HPV vaccination may extend beyond cancer prevention.”
Jiayao Lei
Senior author Jiayao Lei stated that even a relatively small reduction in the risk of preterm birth can be significant at a population level, given that HPV vaccination is administered to millions of young people worldwide
as detailed by Medical Daily.
Early Vaccination Increases Maternal Protection
The protective association proved strongest among women who received their immunization before turning 17, the median age of first sexual intercourse in Sweden. Among this younger subset, the risk of premature delivery dropped by 10 percent reported CIDRAP.
Immunizing adolescents before they encounter the virus prevents initial cervical infections entirely. Zhongsong Zhang, a doctoral student at the Karolinska Institute and lead researcher on the project, explained that the team expect the potential reduction in adverse pregnancy outcomes to become more apparent as cohorts with higher vaccination coverage, particularly those vaccinated at younger ages, reach childbearing age
noted CIDRAP.
Cervical Health Affects Fetal Outcomes
Chronic viral infections of the cervix can cause cervical cancers or precancers. Researchers say the benefits of HPV vaccination may lie directly through prevention infection with the virus and also indirectly through the need for cervical excisional treatment according to News Medical.
Rebecca Perkins, an obstetrician, gynecologist, and investigator at Tufts Medical Center who was unaffiliated with the study, reported CIDRAP that HPV may put pregnancies at risk in multiple ways.
“Infection-related risks may arise from inflammation or placental dysfunction.”
Rebecca Perkins, MD, Tufts Medical Center
Because the investigation relied on observational registry data, authors cautioned that individual-level protective effects cannot be definitively guaranteed, and residual confounding factors like smoking cannot be entirely ruled out noted News Medical.
Public health officials emphasize that incorporating these reproductive benefits into future policy evaluations strengthens the economic and clinical justification for routine adolescent immunization programs worldwide.
Whether individual-level protective effects can be definitively guaranteed remains unknown.