Amniotomy and the use of oxytocin in labor in nulliparous women

A group of 242 nulliparous women in spontaneous, term, first-stage, true labor, with cephalic presentations and intact membranes, underwent amniotomy in the first stage. Sixty-nine of 242 (29%) received oxytocin prior to complete dilatation. The group that received oxytocin was characterized by fewer women less than 20 years of age, more patients with an additional diagnosis such as preeclampsia, longer labors, and slower mean rates of dilatation before and after amniotomy. There was no correlation between the last dilatation rate before and the first after amniotomy. The only significant predictors of oxytocin use were cervical dilatation at amniotomy and the first rate of dilatation afterward. Of patients with dilatation at a rate of greater than or equal to 1 cm/hr from admission to amniotomy, 16% received oxytocin; if less than 1 cm/hr, 39%. Two different rate standards were used to differentiate "unsatisfactory" from "satisfactory" labor: (1) less than 1 or greater than or equal to 1 cm/hr and (2) no change or some change in dilatation. Neither of these standards, when applied to the first examination after amniotomy, predicts patients who will receive oxytocin with any reasonable degree of efficiency. Examination of cervical dilatation after amniotomy in patients who did not receive oxytocin demonstrated failure of the cervix to dilate in approximately 20% of each of three sequential examinations. Contrariwise, no dilatation for 2 hours was uncommon. Amniotomy appears to enhance the dilatation rate in patients with well-dilated cervices that are already dilating at a satisfactory rate and slows dilatation in some patients, particularly those with cervices that are less dilated. These results suggest that amniotomy should be performed for specific indications only.