Human papillomavirus vaccinations' impact on preterm birth rates

Removal of human papillomavirus (HPV) infection associated precancerous cervical lesions by conization is one of the most important causes of preterm birth. Prophylactic HPV-vaccinations can prevent these lesions and reduce the need of their ablative treatment, thereby preventing preterm births. We evaluated whether preterm birth rates vary between HPV-vaccinated and unvaccinated women. Study subjects comprised 6200 cluster-randomized cohorts of HPV-vaccinated and 1667 hepatitis B-virus vaccinated women born in 1992-1993, and age- and community-aligned reference cohort of 19 473 unvaccinated women born in 1990-1991. Age-aligned registry linkage data from the nationwide Finnish Medical Birth Registry were retrieved up to 2018 (older age cohorts) and 2020 (younger age cohorts). Preterm births were categorized as early (gestational age of 22 + 0-33 + 6 weeks) and late preterm births (gestational age 34 + 0-36 + 6 weeks). Logistic regression was used to evaluate the association of HPV-vaccination and preterm births. By the age 28, 23.9% (n = 1484) of HPV-vaccinees and 28.4% (n = 6006) of the unvaccinated women had at least one childbirth recorded. Precisely, 4.1% (n = 61) of HPV-vaccinated and 5.2% (n = 310) of unvaccinated primiparas had a preterm birth. The association of preterm birth with HPV-vaccination was protective with a borderline significant odds ratio of 0.79 (95% CI 0.59-1.04). Most preterm births were at late preterm among both HPV-vaccinees (3.1%) and unvaccinated women (3.4%). Prophylactic HPV-vaccination is likely to reduce the incidence of preterm births. The decrease of preterm births is crucial to reduce the need for extensive and costly postnatal care and life-long morbidity.