Ultrasound assessment of cervical length in prolonged pregnancy: prediction of spontaneous onset of labor and successful vaginal delivery.

OBJECTIVES

To evaluate the usefulness of sonographic assessment of cervical length in the prediction of spontaneous onset of labor and of vaginal delivery.

METHODS

Two hundred and six women who attended a dedicated postdates clinic at 41 + 3 weeks of pregnancy and agreed to the assessment of cervical length using transvaginal ultrasound imaging were included in the study. Those who had not delivered at 42 weeks were offered induction of labor. The labor details were recorded prospectively, and the onset of spontaneous labor and mode of delivery were correlated with cervical length data.

RESULTS

Women who underwent spontaneous onset of labor (n = 112) had a significantly shorter cervical length (mean (SD) 25.0 (8.3) mm) than had women whose labor was induced (n = 67; mean (SD) 29.7 (8.5) mm). Logistic regression analysis showed that cervical length was an independent predictor of the likelihood of spontaneous labor in nulliparous women, and of vaginal delivery in both nulliparous and parous women. Parity had no independent effect on the onset of spontaneous labor, but was an independent predictor of the likelihood of vaginal delivery.

CONCLUSIONS

Sonographic assessment of cervical length is a significant independent predictor of the likelihood of the onset of spontaneous labor in nulliparous women, and of successful vaginal delivery in both nulliparous and parous women with prolonged pregnancy.