Transvaginal sonography of the uterine cervix prior to labor induction.

OBJECTIVES

To compare the Bishop score and transvaginal sonographic measurement of cervical length for predicting the mode of delivery following medically indicated induction of labor in term patients.

METHODS

The study was conducted prospectively in 179 women who required medically indicated induction of labor. Inclusion criteria were singleton pregnancy, gestational age > 37 weeks of amenorrhea, cephalic presentation and intact fetal membranes. Cervical length was measured upon arrival in the labor room but was not considered when choosing the induction procedure. Two receiver-operating characteristic curves were plotted to calculate the best threshold value for the Bishop score and for cervical length for predicting the risk of Cesarean section.

RESULTS

Fifty-three women (29.6%) had a Cesarean section. The Bishop score was not predictive of the delivery mode, although Cesarean section for failure to progress was more frequent when the Bishop score was < or = 5. Among the women with a Bishop score > 5, the cervical length was not predictive of the induction outcome. However, among the women with a Bishop score < or = 5, a cervical length < 26 mm was associated with a lower Cesarean section rate (20.6 vs. 42.9%; P = 0.006). Furthermore, the interval between the beginning of cervical ripening and delivery was shorter in the case of a short cervix (11.01 +/- 6.7 vs. 18.55 +/- 7.07 h; P < 10(-5)).

CONCLUSION

The length of the uterine cervix, measured by transvaginal sonography, is a better predictor of the risk of Cesarean section than the Bishop score after induction of labor for medical reasons. In women with an unfavorable Bishop score, a cervical length of < 26 mm is associated with a lower risk of Cesarean section and a shorter duration of labor.