507: Characterization of labor in term, nulliparous women with singleton, vertex gestations using different statistical models

To characterize the median labor curves of women presenting in spontaneous labor using methods described by Friedman, Zhang, and a constant percent change model. Retrospective chart review of nulliparous, term, singleton vertex (NTSV) presentation in spontaneous labor and delivering vaginally admitted from September 2011 and August 2012. Each cervical exam obtained in labor was recorded. Labor curves were constructed for each group using versions of the Friedman and Zhang models as well as a model assuming constant percent change. Model fit statistics were compared across the three models. 551 NTSV women who presented in active labor and delivered vaginally. These patients presented with a median cervical dilation of 3.5 cm. Using the percent change model, they had a mean 11.0% (±3.8%) change in cervical dilation per hour throughout almost the entire course of labor corresponding to an average of 0.30 cm/hr in early labor and 0.87 cm/hr later with a mean labor time of 22 hours. The corresponding mean rates using the Friedman model were 0.35 cm/hr and 0.92 cm/hr respectively corresponding to a mean total duration of labor of 20.7 hours. In comparison, Zhang's model demonstrated a mean length of labor of 21 hours. The R square values for the percent change, Friedman and Zhang models were 0.868, 0.871 and 0.877 which were not significantly different. There has been recent interest to re-evaluate the progress and management of labor due to rising cesarean rates. We applied three different models to devise median labor curves for our population and conclude that each of the models provides a similar result. These findings suggest that historical and contemporary labor curves are similar based on empirical data and differences in study population and clinical management. Hence, more effort is needed in understanding labor management if efforts to reverse cesarean trends are to be achieved.