Use of the angle of progression on ultrasonography to predict spontaneous onset of labor within 7 days

Objective: To investigate the relationship between angle of progression (AoP) on ultrasonography at 37-40 weeks' gestation and delivery within 7 days. Methods: This prospective study was conducted between January 2013 and May 2013 at Korea University Guro Hospital, Korea. Nulliparous women between 37/0 and 40/3 weeks' gestation with a singleton fetus, intact membrane, and cephalic presentation from January 2013 to May 2013 were enrolled. To evaluate the cervical parameters of cervical length and AoP, transvaginal and transperineal ultrasonography were performed, respectively. We then assessed the relationship between cervical parameters and onset of labor within 7 days by multivariate logistic regression analysis. Results: Women who underwent spontaneous onset of labor within 7 days had a significantly shorter cervical length and AoP than those who underwent labor after 7 days. Logistic regression analysis showed that a larger AoP was an independent predictor of spontaneous labor within 7 days. Conclusions: A larger AoP was significantly associated with spontaneous onset of labor within 7 days. These findings may be useful for counseling patients regarding the management of term pregnancies.