HPV vaccination linked to lower risk of preterm birth
Women who had been vaccinated against HPV had a lower risk of preterm birth than unvaccinated women, according to a large Swedish registry study. The findings build on previous research from Gothenburg showing an association between HPV infection and preterm birth.
HPV is a very common infection that most people acquire at some point in their lives. Since 2012, HPV vaccination for girls has been part of Sweden’s national childhood vaccination program, primarily to prevent cervical cancer. Today, the vast majority of girls are vaccinated.
“What is particularly interesting is the potential public health significance of these findings. We see an association between HPV vaccination and a lower risk of preterm birth. If that association reflects a protective effect of vaccination, the implications could be substantial,” says Bo Jacobsson, Professor of Obstetrics at Sahlgrenska Academy, University of Gothenburg, and Senior Consultant at Sahlgrenska University Hospital.
The study is published in the journal The BMJ and was led by researchers at Karolinska Institutet, the University of Gothenburg, and Sahlgrenska University Hospital.
Lower risk among vaccinated women
The researchers examined the association between HPV vaccination and several pregnancy and birth complications, including preterm birth, preterm rupture of membranes, small for gestational age, stillbirth, and neonatal mortality.
The study is based on Swedish registry data and includes 624,713 pregnancies among first-time mothers aged 16–35 between 2006 and 2023. Of these, 92,620 women had received the quadrivalent HPV vaccine before pregnancy.
Women vaccinated before pregnancy had lower risks across the outcomes studied. The association was most pronounced for preterm birth. Compared with unvaccinated women, vaccinated women had about a 5 percent lower risk of preterm birth and about a 15 percent lower risk of very preterm birth. The association was particularly strong among women vaccinated before age 17.
Building on previous findings
The new study builds on previous research into the association between HPV and preterm birth. A large Swedish registry study published in 2021, involving several researchers from Gothenburg, found an association between HPV infection shortly before or during pregnancy and an increased risk of preterm birth and preterm rupture of membranes, among other outcomes.
At the time, the researchers identified vaccinated groups as an important next step for research, to investigate whether outcomes including preterm birth were less common following HPV vaccination.
Verena Sengpiel, Professor of Obstetrics at Sahlgrenska Academy, University of Gothenburg, and Senior Consultant at Sahlgrenska University Hospital:
“This is a direct continuation of that research. We previously found that HPV infection was associated with an increased risk of preterm birth. Now we see that women vaccinated against HPV also have a lower risk of preterm birth. The findings are entirely consistent with the hypothesis we have been working from,” she says.
Study cannot establish causality
The researchers accounted for several factors that could influence the results. However, because this is an observational study, the findings cannot establish that HPV vaccination is responsible for the lower risk.
Cecilia Kärrberg, Senior Consultant in Obstetrics and Gynecology at Sahlgrenska University Hospital and a researcher affiliated with the Institute of Clinical Sciences at the University of Gothenburg:
“The findings strengthen the hypothesis that HPV infection may help explain the increased risk of preterm birth. But this is an observational study, and we cannot establish a causal relationship. Further research is needed to understand the underlying mechanisms,” she says.
