Effect of Amniotic Membrane Rupture on Length of Labor

Between January 1, 1979, and December 21, 1982, 2564 medically and obstetrically normal patients, admitted to the hospital with intact amniotic membranes during the latent phase of labor, were matched for spontaneous or artificial rupture of the membranes at similar cervical dilations. Spontaneous rupture of the membranes occurred earlier and was more likely in the latent phase of labor than was artificial rupture of membranes, which tended to occur nearer to or in the active phase of labor, and at lower pelvic stations. When matched by cervical dilation, spontaneous membrane rupture was associated with more rapid cervical dilation. Stepwise regression analysis confirmed that membrane rupture had a significant but small effect on labor length and rate of cervical dilation. Pelvic station and maternal parity had a smaller association with labor length than did membrane rupture. Cervical dilation at the time of membrane rupture appeared to be the most important factor associated with the length of labor.