Ultrasonographic cervical length and risk of hemorrhage in pregnancies with placenta previa

Objective: To estimate the relationship between cervical length and hemorrhage leading to preterm delivery in women with placenta previa. Methods: Between October 2007 and May 2009, transvaginal cervical-length measurements were obtained in all singleton pregnancies with placenta previa identified at or beyond 24 weeks of gestation. Only women who delivered liveborn or stillborn neonates at our hospital and had placenta previa confirmed at delivery were included. Cervical length of 30 mm or less was considered short. Clinicians were blinded to cervical-length measurements. Chi-square and logistic regression were used for analysis. Results: Of 89 identified women with placenta previa at initial ultrasonography, 68 had placenta previa at delivery, and 29 (43%) of these had a short cervix. Gestational age at cervical-length measurement was 32±4 weeks in women with a short cervix and 33±2 weeks in those with a longer cervix (P=.4). Women with previa and a short cervix were more likely to require delivery for hemorrhage, 79% compared with 28%, and to deliver preterm, 69% compared with 21% (both P<.001). Tocodynamometer evidence of regular uterine contractions was more common with a short cervix than with a longer cervix, 69% compared with 21% (P<.001). Conversely, 64% with a cervical length greater than 30 mm had no bleeding episodes and progressed to term. Conclusion: In pregnancies with placenta previa, a third-trimester cervical length of 30 mm or less is associated with increased risk for hemorrhage, uterine activity, and preterm birth.