Having received the human papillomavirus (HPV) vaccine before pregnancy is associated with a lower risk of major pregnancy complications including preterm birth, with the greater reduction in risk seen among women vaccinated at an earlier age, finds a large Swedish study published by The BMJ today.
The findings suggest that the benefits of HPV vaccination may extend beyond cancer prevention to the reduction of adverse pregnancy outcomes, say the researchers.
HPV is one of the most common sexually transmitted infections. The quadrivalent HPV vaccine targets four types of HPV, including two (HPV types 16 and 18) that are responsible for about 70% of all cervical cancers. Growing evidence indicates that HPV infection, and the methods used to treat cervical lesions caused by HPV, are linked to an increased risk of pregnancy complications, including preterm birth, so preventing HPV holds potential benefits.
To explore this further, researchers in Sweden used data from nationwide Swedish registers to evaluate the association between quadrivalent HPV vaccination before pregnancy and subsequent risk of adverse pregnancy outcomes.
Their findings are based on 624,713 singleton, first-time births among women aged 16-35 years in Sweden between 2006 and 2023, of whom 92,620 (15%) had received quadrivalent human papillomavirus vaccination before pregnancy.
Cases were women with at least one adverse pregnancy outcome, including preterm birth (before 37 weeks), very preterm birth (28 to 31 weeks), preterm and/or prelabor rupture of membranes, delivering a small or severely small baby, stillbirth, or newborn death.
Each case was matched with up to 10 control women of the same age and year of conception and a range of other potentially influential factors were taken into account including self-reported cigarette smoking and body mass index at first antenatal visit, maternal diagnoses and assisted reproduction, mother's country of birth, family income and education level.
After accounting for these factors, quadrivalent HPV vaccination was associated with lower odds of all included adverse pregnancy outcomes, compared with no vaccination.
Statistically significant associations were seen for preterm and very preterm birth, spontaneous preterm birth, preterm prelabour rupture of membranes, and delivering a severely small baby. Risk reduction was generally more pronounced among women vaccinated before age 17.
This is an observational study so no firm conclusions can be drawn about cause and effect, and the authors acknowledge incomplete information on spontaneous abortions, and limited investigation of the underlying clinical pathways. Nor can they rule out the possibility that other unmeasured factors may have affected their results.
However, they say this large study based on high quality data with long follow-up in a real world setting minimised bias and misclassification, enabling assessment of both common and rare adverse pregnancy outcomes. And results were similar after further analyses, suggesting that they are robust.
As such, they say: "Together with previous research showing the safety of human papillomavirus vaccination during pregnancy, our results suggest that human papillomavirus vaccination is not only safe with respect to pregnancy outcomes but may also confer additional benefits by reducing the risk of adverse events."
"Collectively, this evidence supports the global strategy for human papillomavirus vaccination and its continued implementation in routine immunisation programmes," they add.
