Association of second-trimester cervical length with prolonged pregnancy

OBJECTIVE: To estimate whether there is an association between second-trimester cervical length and prolonged pregnancy (defined as delivery at or beyond 41 weeks of gestation). METHODS: This is a cohort study of nulliparous women with a singleton pregnancy who underwent routine cervical length measurement between 18 and 24 weeks of gestation. Women were divided into quartiles by cervical length and the association with prolonged pregnancy was evaluated in bivariable and multivariable analyses. A planned secondary analysis included only women who achieved at least 39 weeks of gestation. RESULTS: During the study period, a total of 9,165 women met inclusion criteria, of whom 1,481 (16.2%) had a prolonged pregnancy. Women in increasing cervical length quartiles were more likely to experience a prolonged pregnancy (12.9%, 15.8%, 17.1%, 18.6%, P<.001). This association remained significant when controlling for possible confounding variables. An analysis confined to women who achieved at least 39 weeks of gestation was consistent with the overall analysis. CONCLUSION: Increasing second-trimester cervical length is associated with an increased likelihood of having a prolonged pregnancy in nulliparous women.