Study revisits what "normal" labor means

Ideas about what constitutes "normal" labor progression and labor "arrest" may require revision, according to the findings of a recent multicenter retrospective study. Researchers from the National Institutes of Health found that among a large contemporary population of women in the United States, progress from 4 cm to 6 cm of dilation was far slower than what is perceived to be normal.

The Consortium on Safe Labor study included more than 62,000 women with a singleton term gestation, spontaneous onset of labor, vertex presentation, vaginal delivery, and a normal perinatal outcome. Using electronic medical records from 19 US hospitals, the authors found that women frequently take more than 6 hours to progress from 4 cm to 5 cm and more than 3 hours to progress from 5 cm to 6 cm, regardless of parity. Although labor accelerates much faster after 6 cm in all women, it does so more for multiparous women; thus, although no appreciable change in dilation for 4 hours may be normal in early labor, it is probably not normal after 6 cm. The 95th percentiles of the second stage of labor in nulliparous women with and without epidural analgesia were 3.6 hours and 2.8 hours, respectively.

Researchers also found that even in women with rapid cervical dilation in the late first stage, the active phase often did not start until dilation had attained 6 cm or more.

Zhang J, Landy HJ, Branch DW, et al. Contemporary patterns of spontaneous labor with normal neonatal outcomes. Obstet Gynecol. 2010;116(6):1281–1287.