Prelabor evaluation of inducibility.

Data were collected prospectively on 381 patients admitted for stimulation of labor because of premature rupture of the membranes and 808 patients for induction of labor. The induction was by primary amniotomy in 337 cases, and the remaining 471 cases, because of relatively unfavorable cervical conditions, were treated without primary amniotomy. Induction of labor failed on the first day in 181 of the cases with an unfavorable cervix. All patients were delivered vaginally of one living infant in cephalic presentation. The predictive value of the Bishop pelvic score and other factors regarding the duration of labor (induction-delivery time) and the inducibility of labor (latency period) were evaluated by multiple regression analyses. The influence of parity on duration of labor was found to be very constant and highly significant, whereas it seemed to have only little influence on inducibility. The only factor of significant importance to inducibility thus seems to be the prelabor cervical condition. Of the 5 components in the Bishop score, dilatation was found to be most important and should be weighted at least twice the value given it by Bishop. A new pelvic score for prelabor evaluation of inducibility is proposed on the basis of these results.