HPV Vaccine Before Pregnancy May Lower Preterm Birth Risk

The HPV vaccine is best known as a shield against cervical cancer. A major new study suggests it may do more: protect future pregnancies too. Researchers at Karolinska Institutet in Sweden report that women who received the HPV vaccine before becoming pregnant had lower odds of preterm birth and several other complications, according to findings published in The BMJ.

The study drew on Swedish national registers covering more than 600,000 singleton births among first-time mothers aged 16 to 35, between 2006 and 2023. About one in seven of the mothers had received the quadrivalent HPV vaccine before conceiving, giving the researchers a rare chance to compare pregnancy outcomes at population scale.

What the Swedish HPV vaccine study found

The team used a matched case-control design: for each birth with a complication, they selected up to ten comparison births from women of the same age who conceived in the same calendar year. They then adjusted for factors that could skew the picture, including smoking, body weight, income, education, assisted reproduction, and where the mother was born, as reported by News-Medical.

After those adjustments, vaccination was linked to lower odds of every adverse outcome examined. The statistically significant findings linked to the HPV vaccine included preterm birth before 37 weeks, very preterm birth between 28 and 31 weeks, spontaneous preterm birth, and preterm rupture of membranes. Women who were vaccinated were roughly five percent less likely to give birth prematurely, and roughly 15 percent less likely to deliver very prematurely, than unvaccinated women.

Severely small-for-gestational-age babies also turned up less often in the vaccinated group. Each case was drawn from the full national birth register, which the authors say minimized bias and allowed them to examine both common and rare complications.

How the HPV vaccine might protect pregnancies

The biological explanation starts with what HPV does to the cervix. Persistent infection with high-risk HPV types is the primary cause of cervical precancer and cancer, and both the infection and the excisional treatments used to remove precancerous lesions have been tied to a higher risk of preterm birth. By preventing infection early, vaccination may keep the cervix healthier going into pregnancy.

Sweden's rollout history made the study possible. The first HPV vaccine arrived in 2006, subsidized vaccination for girls aged 13 to 17 followed, and a free school-based program for girls aged 10 to 12 began in 2012. Since 2020 the school program has been gender-neutral. That long timeline let researchers track women from adolescence through their first pregnancies.

The timing finding was the most striking. According to lead author Zhongsong Zhang, a doctoral student at Karolinska Institutet, the protective link was stronger among women vaccinated before the age of 17, which he said fits earlier evidence that the shot works best when given young. Earlier vaccination means the body builds immunity before first exposure to the virus.

Why this matters for young people now

For Gen Z, the takeaway is about timing. Global health guidelines already recommend the shot in early adolescence, and this study adds a reproductive reason on top of the cancer argument. Catch-up vaccination is possible later, but the benefit appears largest when the doses come early.

The results also speak to a persistent vaccine worry. Fears that the HPV shot harms fertility have circulated for years, and large reviews have found no such effect. This study goes a step further, suggesting the shot is not only safe with respect to pregnancy outcomes but may carry an added benefit — a point the authors say supports continued rollout of routine immunization programs.

One important caveat: the study is observational, so it cannot prove the vaccine caused the lower risk. The researchers acknowledge that unmeasured factors could still play a role, and they had incomplete information on early miscarriages. They also could not fully pin down the clinical pathway linking the shot to healthier births. Still, the association held up across multiple analyses, and similar hints have surfaced in register studies from Denmark, Australia, Finland, and Scotland.

Preterm birth remains one of the leading global causes of newborn death, and effective prevention options are limited. If even a modest reduction holds across millions of vaccinated young people worldwide, the authors argue, the population-level gain could be substantial. For more on the HPV vaccine and reproductive health, explore our sexual wellness and health coverage.