A reappraisal of the duration of labor.

The mean, median, and modal durations of labor have been established following a prospective study of 602 consecutive labors. The mean duration of labor for primiparae was 14.92 hours, while the median and modal durations were 13.20 and 9.66 hours, respectively. The corresponding figures for multiparae were 10.02, 9.28, and 7.80 hours, respectively. There was a statistically significant difference in the mean duration of labor in the 2 groups of patients (P less than 0.001). A significant positive correlation has been observed between the duration of the first stage of labor and the second stage of labor (P less than 0.001), and this might be of clinical importance. It has been suggested that the median and modal durations of labor may be more representative and informative than the mean or average.