HPV Vaccination Before First Pregnancy Linked to 15% Lower Odds of Very Preterm Birth in Swedish Registry Data

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Different Workouts Suited Different MarkersA pooled analysis of 53 trials found that different exercise types helped different metabolic markers. Most of the evidence was low certainty. JEAN-PHILIPPE KSIAZEK | AFP via Getty Images Share on Twitter Share on Facebook Share on Pocket Women who received the HPV vaccine before their first pregnancy were less likely to give birth very early, according to a large Swedish study published Oct. 7 in The BMJ. Vaccinated mothers had 15% lower odds of very preterm birth, defined as delivery from 28 weeks to just under 32 weeks, a stage when newborns often need weeks of intensive care.

The study does not prove the vaccine prevented those early births. But it adds a new layer to a familiar family decision, since the HPV shot is usually given years before pregnancy is on anyone’s mind. Senior author Jiayao Lei said the results suggest “the benefits of HPV vaccination may extend beyond cancer prevention.”

The finding comes as U.S. preterm birth rates remain high. About 10.41% of U.S. babies were born preterm in 2025, unchanged from 2024, according to provisional data from the CDC’s National Center for Health Statistics.

Researchers at Karolinska Institutet and the University of Gothenburg analyzed national registry data on 624,713 single births to first-time mothers ages 16 to 35 between 2006 and 2023. Of those women, 92,620, or 14.8%, had received at least one dose of the four-type (quadrivalent) HPV vaccine before conceiving.

After adjusting for factors including smoking, body weight, income, and education, vaccinated women had about 5% lower odds of any preterm birth and 15% lower odds of very preterm birth. They also had modestly lower odds of spontaneous preterm labor and severely undersized newborns. A slightly lower rate of early rupture of the membranes was at the edge of statistical significance.

The pattern was strongest in women vaccinated before 17, the median age of first sexual intercourse among Swedish women. “We also observed that the associations were stronger among women who had been vaccinated before the age of 17,” said first author Zhongsong Zhang, a doctoral student at Karolinska, in a Karolinska Institutet statement.

The researchers described two ways the vaccine could plausibly matter. HPV infection itself has been tied to higher preterm birth risk in earlier studies, and lab research suggests the virus may impair early embryo development and the function of cells that form the placenta. Preventing infection could, in theory, remove that strain on a pregnancy.

The second pathway involves treatment. Women with precancerous cervical changes often have tissue removed from the cervix, a procedure linked to roughly double the risk of spontaneous preterm birth. When the team accounted for high-grade cervical lesions in an exploratory analysis, the links to preterm birth weakened. That is consistent with this explanation, though it does not prove it.

Lei, an assistant professor at Karolinska, put the scale in perspective. “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 said.

The Swedish results fit a pattern seen elsewhere, though not every study agrees. A Danish registry study of more than 240,000 births found that women vaccinated before 17 had a lower risk of spontaneous preterm birth, while those vaccinated later did not. Two Finnish studies tied to a vaccine trial also reported fewer preterm births among vaccinated women, but they included relatively few pregnancies.

A study of about 11,000 births in Aberdeen, Scotland, found no link with preterm birth, though it did find lower rates of early membrane rupture. The Swedish team matched mothers by age and year of conception to help account for changes in vaccine uptake, cervical screening, and obstetric care over time.

Timing in Sweden also shaped the results. Subsidized vaccination for girls ages 13 to 17 began in 2007, and a free school-based program for girls ages 10 to 12 started in 2012. Many mothers in the study were vaccinated through catch-up programs, and some may already have been exposed to HPV, which the authors said could make the measured benefit smaller than it would be for children vaccinated today.

MedicalDaily Evidence Check: This was an observational, nationwide registry-based case-control study, not a clinical trial. It was peer-reviewed and covered more than 624,000 births. It found an association between prior HPV vaccination and fewer early births, but hidden differences between vaccinated and unvaccinated women, such as health habits or access to care, cannot be ruled out.

The study also lacked information on whether vaccinated women later caught HPV or had cervical treatment. The effects were modest. In a sensitivity analysis, the researchers estimated that about 518 women would need to be vaccinated to prevent one preterm birth.

Funding came from Swedish public research bodies and the Swedish Cancer Society. The results involve the older four-type vaccine, while the United States now uses Gardasil 9, which covers nine HPV types.

For U.S. households, the practical question is about timing rather than pregnancy itself. HPV vaccination remains among the immunizations recommended for all children, which insurers must cover without cost-sharing, according to a January 2026 CDC announcement on the updated childhood immunization schedule.

The Society of Gynecologic Oncology said the revised schedule now recommends a single dose and that payers will no longer be required to cover additional doses. The group added that coverage of extra doses after 2026 is unclear.

Parents can check a child’s vaccination record with their pediatrician or state immunization registry. Young adults who missed the vaccine can ask a clinician whether catch-up vaccination makes sense. The CDC advises against HPV vaccination during pregnancy, so anyone already pregnant should wait until after pregnancy.

Pregnant people who notice regular contractions, pelvic pressure, fluid leakage, or bleeding before 37 weeks should contact their obstetric provider right away. The new findings do not change current medical guidance, and researchers say longer follow-up of vaccinated generations will help clarify the size of any benefit.

Does the HPV vaccine prevent preterm birth?

That has not been proven. The Swedish study found vaccinated women had lower odds of preterm and very preterm birth, but because it was observational, it cannot show the vaccine caused the difference.

Vaccinated women had about 5% lower odds of any preterm birth and 15% lower odds of very preterm birth, defined as delivery from 28 weeks to just under 32 weeks. The links were stronger in women vaccinated before age 17.

Can I get the HPV vaccine while pregnant?

HPV vaccination is not recommended during pregnancy. People who are pregnant or planning a pregnancy should discuss timing with their clinician.

Researchers point to two possible pathways: preventing HPV infection, which has been tied to preterm birth, and reducing the need for cervical procedures that raise the risk of early delivery.

Does this change U.S. vaccine recommendations?

No. HPV vaccination remains on the federal schedule recommended for all children, and the study does not change current guidance for pregnant people or parents.