Sonographic cervical length, vaginal bleeding, and the risk of preterm birth.

OBJECTIVE: We sought to evaluate the contributions of vaginal bleeding and cervical length to the risk of preterm birth.

STUDY DESIGN: This was a secondary analysis of a cohort study designed to study predictors of preterm birth. The study included 2988 women with singleton gestations. Women underwent midtrimester transvaginal ultrasound assessment of cervical length and were queried regarding first- and second-trimester vaginal bleeding.

RESULTS: There was a significant second-order relation between cervical length and preterm birth (P < .001, P = .005). Women with vaginal bleeding were at higher risk of preterm birth (odds ratio, 1.5; 95% confidence interval, 1.3-2.0). There was a significant interaction between cervical length and vaginal bleeding (P = .015). After accounting for cervical length and interaction, the adjusted odds ratio for vaginal bleeding and preterm birth was 4.8 (95% confidence interval, 1.89-12.4; P = .001).

CONCLUSION: The magnitude of risk of preterm birth associated with sonographic cervical length depends on a woman's history of first- and second-trimester vaginal bleeding.