Have curves for spontaneous labor really changed?

Rates of cesarean delivery have risen, and with them, interest in determining what influence-if any-progress and management of labor have on the uptick.  A retrospective chart review presented at the 34^th Annual Meeting of the Society for Maternal-Fetal Medicine: The Pregnancy Meeting suggests that labor curves are unchanged and a better understanding of labor management is needed to reverse the cesarean trend.

Coauthored by Contemporary OB/GYN Editorial Board member Sarah J. Kilpatrick, MD, PhD, the study characterized median labor curves in 551 nulliparous women with singleton vertex presentations who presented in spontaneous labor and delivered vaginally between  September 2011 and August 2012. Each cervical exam obtained during labor was recorded and labor curves were constructed using Friedman, Zhang, and a constant percent change model. Model fit statistics were compared across all three models.

Median cervical dilation was 3.5 cm. Throughout almost the entire course of labor, the mean change in cervical dilation per hour was 11.0% (±3.8%) with the percent change model, or an average of 0.30 cm/hr in early labor and 0.87cm/hr in later labor with a mean labor time of 22 hours. Using the Friedman model, dilation time was 0.35 cm/hr in early and 0.92 cm/hr in later labor with a mean labor time of 20.7 hours. The Zhang model had an average labor length of 21 hours. R square values for perfect change, Friedman, and Zhang models were 0.868, 0.871, and 0.877, which were not statistically different.

The study authors concluded that the three models produced similar results, suggesting that historical and contemporary labor curves are much the same based on empirical data and differences in study population and clinical management. 

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