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Though vaginal human papillomavirus (HPV) was often detected in pregnant women, perinatal transmission was infrequent, and no infection at birth persisted half a year later, a prospective cohort study showed.

The virus was detected in 40.2% of 1,050 pregnant women at three Canadian academic hospitals, but the probability of transmission to the baby was estimated at just 7.2% (95% CI 5.0-10.3), Helen Trottier, MSc, PhD, of the Centre de Recherche du Centre Hospitalier Universitaire Sainte-Justine and Université de Montréal, and colleagues reported.

All 22 children who were HPV-positive at birth cleared the infection before they reached 6 months of age, the researchers wrote in .

"As HPV testing becomes popular as a screening test for cervical cancer, it is likely that many women will test positive during pregnancy. Our results are important to reassure pregnant women: the risk of transmission of HPV to their new baby is low," Trottier told MedPage Today in an email.

The low rate of HPV detection in newborns was not surprising, "but what is less known is the risk of HPV persistence in children," Trottier added. "There is always the question of whether the HPV found in newborns has really been eliminated or if some of the virus has remained undetected in the basal cells and can reactivate later in childhood. It is important to continue the research, but we can say that the data of our study are all the same reassuring."

Participants in the study were pregnant women ages 18 and older who were at 14 weeks or earlier of gestation. The participants were recruited between Nov. 8, 2010, and Oct. 16, 2016. Laboratory and statistical analysis were completed on Nov. 15, 2022.

Among 422 women HPV-positive at their first trimester visit, 280 (66.4%) were infected with at least one high-risk genotype. Co-infections were frequent, with 190 women (45.0%) harboring at least two genotypes.

Notably, HPV was detected in 10.7% of placentas, but only 3.9% of biopsies on the fetal side under the amniotic membrane were positive.

In cases of transmission to children, the most common sites of infection were the conjunctiva (3.2%, 95% CI 1.8-5.6), followed by the mouth (2.9%, 95% CI 1.6-5.2). HPV detection on genital surfaces was 2.7% (95% CI 1.4-4.9). And in the pharynx, it was 0.8% (95% CI 0.2-2.5).

The mean and median time of clearance for HPV detected at birth were 3.13 and 3.0 months, respectively.

Most HPV-positive children had at least one of the same genotypes detected in vaginal samples of their mothers during pregnancy. However, new HPV genotypes were detected in eight children at their 6-month visit, they noted.

"Among these children, there were 5 in whom the detected genotype was not detected in the pregnant mother or in the child before, suggesting a possible horizontal transmission," Trottier and colleagues wrote. "On the other hand, among these children, there were two in whom we did not detect HPV before the 6-month visit but who were born to mothers who were positive for these genotypes during pregnancy, as well as one child in whom we detected the genotype at birth (followed by a negative test at the 3-month visit) and who was born to a mother positive for this genotype."

"Although this does not exclude the possibility of horizontal transmission, it is possible that this represents undetected infection in children up to 6 months of age or reactivation of the virus," they added.

The study did have limitations. Repeat testing participants for HPV in the third trimester of pregnancy would have provided "interesting data on HPV dynamics during pregnancy and may have explained certain infections found in placentas and children," Trottier and colleagues wrote.

And despite a large sample size, several HPV genotypes were relatively rare, which precluded genotype-specific analysis, they noted.

"Although our study provides the necessary data for clinicians to be able to reassure HPV-positive pregnant women about the low risk to their babies, it should be remembered that persistent infection by certain types of HPV in pregnant women seems to increase the risk of preterm delivery and is involved in cancers of the cervix, and certain anogenital and oral cancers," Trottier told MedPage Today.

"Vaccination against HPV remains essential to prevent several severe outcomes," Trottier added.

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