Human papillomavirus (HPV) is one of the most common sexually transmitted infections. It also is a threat to women's reproductive health, causing most precancerous cervical lesions and cervical cancers.

Men and women become infected with HPV through sexual contact. Luckily, the HPV vaccine has produced significant public health benefits. In addition to lowering the risk of cervical cancer in women, the vaccine also reduces oral cancers in men.

People who were vaccinated against HPV had a lower risk of preterm birth and preterm leaking of amniotic fluid. They were less likely to have babies who were stillborn or who died during their first month of life.

HPV infection can lead to serious complications during pregnancy. Early investigations in Denmark, Finland, Australia and Scotland had found that women who had been vaccinated against HPV seemed to have fewer pregnancy complications, but the studies were small and lacked large, nationwide data sets.

Using data from multiple health registries, Swedish and Norwegian researchers tracked the pregnancy outcomes of more than 620,000 first-time mothers to see if there was a connection between HPV vaccination and better pregnancy outcomes. The women were between the ages of 16 and 35 years old. More than 92,600 of them had received the HPV vaccine before becoming pregnant.

The large sample revealed that having had an HPV vaccination before pregnancy was linked to a reduced likelihood of a number of pregnancy risks.

Those who were vaccinated against HPV had a significantly lower risk of preterm birth before 37 weeks of pregnancy, including very preterm birth between 28 and 31 weeks. They also were less likely to have preterm leaking of amniotic fluid.

Women who received the vaccine were also less likely to have babies who were small or very small, stillborn or who died during their first month of life. As the researchers said in a statement, “This evidence supports the global strategy for human papillomavirus vaccination and its routine implementation in immunization programs.”

The U.S. Centers for Disease Control and Prevention recommends that children between the ages of 11 and 12 years old get two doses of the vaccine given six months to one year apart.

The greatest reduction in risk to babies was seen among women who were vaccinated at a younger age, before they turned 17 years old.

This was an observational study and shows an association between the HPV vaccine and a reduced risk for poor pregnancy outcomes. It cannot prove that the vaccine alone reduces risk.

In the U.S., the HPV vaccine is distributed under the brand name Gardasil-9 and protects against nine strains of the virus, including the two most linked to cancer. The U.S. Centers for Disease Control and Prevention recommends children between the ages of 11 and 12 years old get two doses of the vaccine given six months to one year apart.

Children can be vaccinated as early as age nine. Few who were vaccinated reported experiencing side effects, and the side effects that were reported were mild.

The study is published in the bmj, the British Medical Journal.