An illustration of human papillomavirusAlexey Kotelnikov/Alamy
Pregnant women infected with the human papillomavirus (HPV), which causes cervical cancer, are nearly four times more likely to give birth prematurely.
The finding suggests that as more teenagers are vaccinated against HPV, there will be fewer premature births, says Helen Trottier at the University of Montreal in Canada. Premature babies are born smaller and are more prone to infections and numerous other health problems.
HPV is a sexually transmitted virus that is shrugged off naturally by most people, but it can linger and cause cervical cancer, as well as anal and throat cancers and genital warts.
Most high-income countries started offering HPV vaccination to teenagers about a decade ago. Rates of genital warts have started falling, although any effect on cervical cancer rates is taking longer to show up, as it takes many years to develop.

Trottier wondered what the effects of the virus would be on pregnant women. Her team tested nearly 900 women for HPV in their vaginal fluid in the first and last three months of pregnancy. About 42 per cent tested positive at the start, and two-thirds of these still had the virus by the end.
Those who had HPV throughout their pregnancy were 3.7 times more likely to either spontaneously go into early labour, or need to be induced to give birth early due to complications, compared with those who tested negative at the start. “We were surprised to see how strong was the association,” says Trottier.
If the virus is directly causing the premature labour, the mechanism is unclear. HPV doesn’t cause inflammation, one known cause of premature births, but it could damage cells of the cervix, making them more vulnerable to bacterial infections that do cause inflammation, says Trottier.
Previous research in Australia, which started offering the HPV jab in 2007, has shown that women from vaccinated age-groups have a lower rate of premature births than older women, suggesting the virus really is directly causing the effect. As vaccine uptake rises, numbers of premature births are likely to fall everywhere, says Trottier. “We will probably see a big impact.”
Journal reference: JAMA Network Open, DOI: 10.1001/jamanetworkopen.2021.25308
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