Prediction of labor and delivery by transperineal ultrasound in pregnancies with prelabor rupture of membranes at term.

Objective: To evaluate whether engagement of the fetal head or cervical length in women with premature rupture of membranes (PROM) at term, are associated with time from PROM to delivery or need for operative delivery.

Methods: A transperineal ultrasound examination was performed in 152 women with a single live fetus in cephalic presentation after PROM (at > 37 gestational weeks). The shortest distance from the outer bony limit of the fetal skull to the skin surface of the perineum was measured in a transverse view, and the cervical length was measured in a sagittal view. The time from PROM to delivery was tested in a Cox regression analysis with ultrasound measurements, parity, maternal age, body mass index and birth weight as possible predictive factors.

Results: The head-perineal distance was associated with the time from PROM to delivery (log rank test, P < 0.001). Thirty-six hours after PROM, 32% (95% CI, 15-49) of women with a short head-perineal distance (< 45 mm) and 43% (95% CI, 24-62) of women with a long distance (> or = 45 mm) were still in labor. Women with a short head-perineal distance had fewer Cesarean sections, less use of epidural analgesia and a shorter time in active labor, and their babies had a higher pH in the umbilical artery. The measured cervical length was not associated independently with time to delivery.

Conclusion: Transperineal ultrasound measurements of fetal head engagement may help clinicians to predict the course of labor in women with PROM.