Obstetricians have been trained to expect labor to progress faster than it actually does, which may be the reason for the high rate of inductions and c-section deliveries in the US according to a new report.  The study published in Obstetrics & Gynecology used information from over 62,000 normal, natural births and figured out the average labor time for dilation from 4 to 5 cm, 5 to 6 cm, and over 6 cm.  Most cases of "failure to progress," which is the number one reason for inductions, occur during this part of the first stage of labor.

The authors found that women who had given birth before progress much quicker once they reach the 6 cm mark than women who were giving birth for the first time.  The progression from 4 to 5 cm and 5 to 6 cm went much slower for both groups of women than earlier studies have shown.  The established obstetrics benchmark based on those earlier studies created an expectation for a much quicker progression through active labor than what this report found. The researchers also pointed out that spinal nerve anesthetics also may be delaying the second stage by 29%, with an average labor time of 3.6 hours with an epidural and 2.8 hours without it. 

The authors proposed an updated model of labor progression for new moms based off their research.  They feel that, if OBs were to follow their new model and allow labor to continue for longer in the lead up to the 6 cm mark, it may reduce the number of interventions, c-sections, and subsequent repeat cesarean deliveries in the US.

Zhang, Jun PhD, MD; Landy, Helain J. MD; Ware Branch, D. MD et al (2010). "Contemporary Patterns of Spontaneous Labor With Normal Neonatal Outcomes." Obstetrics & Gynecology 116 (6) pp 1281-87. doi: 10.1097/AOG.0b013e3181fdef6e.