HPV Vaccination Prior to First Pregnancy Linked to Lower Very Preterm Birth Risk

A large Swedish registry study published Oct. 7 in The BMJ found that women who received the HPV vaccine before their first pregnancy had lower odds of very preterm birth. The analysis showed a 15% reduction in the likelihood of delivery between 28 and 31 weeks, a period when infants typically require intensive care.

The research cannot establish causality, but it adds a new dimension to the decision‑making process surrounding HPV vaccination, which is typically administered years before pregnancy. Senior author Jiayao Lei commented that the findings “suggest the benefits of HPV vaccination may extend beyond cancer prevention.”

These results are especially relevant given that the United States continues to face high preterm birth rates. Provisional CDC data indicate that approximately 10.41% of babies were born preterm in 2025, a figure unchanged from 2024.

Inside the Swedish Numbers

Investigators from Karolinska Institutet and the University of Gothenburg examined a nationwide cohort of 624,713 first‑time mothers aged 16‑35 who gave birth between 2006 and 2023. Among them, 92,620 women (14.8%) had received at least one dose of the quadrivalent HPV vaccine prior to conception.

After controlling for smoking status, body‑mass index, socioeconomic indicators, and educational level, vaccinated mothers experienced roughly a 5% reduction in the odds of any preterm birth and a 15% reduction in the odds of very preterm birth. They also showed modestly lower odds of spontaneous preterm labor and of delivering severely growth‑restricted infants. Early rupture of membranes occurred slightly less often, though this difference approached but did not reach conventional statistical significance.

The association was most pronounced among women who received the vaccine before age 17, which coincides with the median age of first sexual intercourse in Sweden. “We also observed that the associations were stronger among women who had been vaccinated before the age of 17,” noted lead author Zhongsong Zhang, a doctoral student at Karolinska Institutet, in an institute press release.

Possible Pathways Through HPV Infection

The investigators proposed two plausible mechanisms. Prior epidemiologic studies have linked HPV infection to an increased risk of preterm birth, and laboratory data suggest that the virus may disrupt early embryonic development and placental cell function. By preventing infection, the vaccine could theoretically eliminate this adverse influence on pregnancy.

A second route involves cervical treatment. Precancerous cervical lesions often require excisional procedures, which have been associated with roughly a two‑fold increase in spontaneous preterm birth risk. In an exploratory analysis that adjusted for high‑grade cervical lesions, the observed association between vaccination and reduced preterm birth diminished, a finding consistent with this hypothesis, though it remains unproven.

Lei, an assistant professor at Karolinska, emphasized the public‑health impact. “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,” she observed.

The Swedish findings echo observations from other nations, although research results are mixed. A Danish registry study of over 240,000 births demonstrated a reduced risk of spontaneous preterm birth among women vaccinated before age 17, with no effect seen for later vaccination. Two Finnish investigations linked to a vaccine trial also reported fewer preterm births in vaccinated cohorts, but both included relatively small numbers of pregnancies.

Conversely, an Aberdeen, Scotland, cohort of roughly 11,000 births identified no association with preterm birth, though it did report lower rates of early membrane rupture. To mitigate temporal confounders, the Swedish researchers matched each mother to controls based on age and year of conception, thereby accounting for shifts in vaccination coverage, cervical‑screening programs, and obstetric practices over the study period.

The timing of vaccination in Sweden also influenced the outcomes. Subsidized HPV vaccination for girls aged 13‑17 was introduced in 2007, and a free school‑based program for girls aged 10‑12 began in 2012. A substantial proportion of the mothers in the cohort received vaccines through catch‑up initiatives, meaning some may have already been exposed to HPV, an exposure that the authors note could attenuate the observed protective effect compared with vaccination administered before any viral exposure.

Evidence Check and Open Questions

MedicalDaily Evidence Check: This was an observational, nationwide registry‑based case‑control study, not a randomized clinical trial. Peer‑reviewed and encompassing over 624,000 births, it identified an association between prior HPV vaccination and a reduced incidence of early deliveries. However, residual confounding—differences in health behaviors, socioeconomic status, or healthcare access between vaccinated and unvaccinated groups—cannot be fully excluded.

The dataset did not capture subsequent HPV infections or cervical‑treatment events among the vaccinated women, and the magnitude of the effects was modest. Sensitivity modeling indicated that approximately 518 women would need to be vaccinated to avert one preterm birth.

Funding was provided by Swedish public research agencies and the Swedish Cancer Society. The investigation focused on the older quadrivalent formulation; current U.S. practice utilizes Gardasil 9, which protects against nine HPV types.

Decisions Facing U.S. Families Now

For U.S. families, the key consideration is the timing of vaccination rather than pregnancy status itself. HPV immunization continues to be listed among the routine childhood vaccines, with insurers required to provide coverage without cost‑sharing, as outlined in a January 2026 CDC update to the childhood immunization schedule.

The Society of Gynecologic Oncology indicated that the revised schedule now advises a single‑dose regimen, and payers are no longer mandated to reimburse additional doses; however, the group noted that coverage for extra doses administered after 2026 remains uncertain.

Parents may verify vaccination status through their child’s pediatrician or the state’s immunization registry. Young adults who did not receive the vaccine earlier can discuss catch‑up vaccination with a health‑care provider. The CDC recommends against administering HPV vaccine during pregnancy, and pregnant individuals should defer vaccination until after delivery.

Individuals who experience regular contractions, pelvic pressure, leakage of fluid, or vaginal bleeding before 37 weeks of gestation should seek immediate obstetric care. The newly published data do not alter existing clinical recommendations, and investigators emphasize that extended follow‑up of vaccinated cohorts will be essential to delineate the full public‑health impact.

Key Questions Answered

Does the HPV vaccine prevent preterm birth?
That has not been proven. The Swedish cohort study observed a lower odds of preterm delivery among vaccinated women, but its observational design precludes definitive causal inference.

How large was the difference?
Vaccinated women had roughly a 5% reduction in the odds of any preterm birth and a 15% reduction in the odds of very preterm birth (delivery before 32 weeks). The association was more pronounced among those who received the vaccine before age 17.

Can I get the HPV vaccine while pregnant?
HPV vaccination is not recommended during pregnancy. Pregnant individuals or those planning pregnancy should discuss timing with their clinician.

Why might the vaccine affect pregnancy?
Researchers propose two mechanisms: preventing HPV infection, which has been linked to preterm birth, and decreasing the need for cervical‑excisional procedures that raise early‑delivery risk.

Does this change U.S. vaccine recommendations?
No. HPV vaccination remains on the federal schedule for all children, and the study does not modify current guidance for pregnant individuals or parents.

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