Transition from latent to active labor.

The transition from the latent to the active phase of labor, as defined by Friedman, was studied in all noncomplicated patients over a four-year period. Mothers studied were in spontaneous labor with a singleton fetus in the vertex position with intact membranes at admission. The independent variables were the parity and vaginal examination data, and the dependent variable was the rate of cervical dilation. The transition from latent to active labor was recorded and stratified by the cervical dilation where it occurred in a sample population consisting of 1060 nulliparous and 639 primiparous or multiparous women. There were no differences between nulliparous and multiparous patients. Less than 50% of labors became active by the time the cervixes had reached 4-cm dilation. By 5 cm, 74% of labors were active. However, when protracted and arrested labors were eliminated, 60% of the patients had reached the latent-active transition by 4 cm and 89% by 5 cm. We concluded that once a normal patient has reached 5 cm, she should be in the active phase of labor. If not, there is a high probability of labor dystocia.