The Natural History of the Normal First Stage of Labor

The inability to reduce the climbing rate of cesarean delivery worldwide is due, in part, to an inadequate understanding of the normal labor process, especially the first stage of labor. Improved diagnostic and interventional procedures are needed to manage women who labor slowly. This multicenter, prospective, observational study investigated patterns of labor in a large population, and assessed an alternative diagnostic approach for abnormal labor progression. The first stage of labor was studied using data from the National Collaborative Perinatal Project collected from 1959 to 1966. A total of 26,836 singleton term pregnancies delivered at 20 weeks or later were included in the final analysis. Other inclusion criteria were spontaneous onset of labor, a vertex fetal presentation at admission, and a normal perinatal outcome. To assess labor progression among nulliparous and multiparous pregnancies, a repeated-measures analysis with an eighth-degree polynomial model was used to construct average labor curves. An interval-censored regression assessed the duration of labor stratified by cervical dilation at admission, and the time for progression centimeter by centimeter.