Zhang et al. also reported that 40% of women who undergo induction of labor get a cesarean section when they are 4 cm dilated. "That’s probably where we really need to start paying some attention to what we’re doing," Dr. King said. Too many cesarean sections are being done at cervical dilations of 6 cm or less, she said.
Other recent data show that women with induced labor need significantly more time to reach 6-cm dilation compared with women with spontaneous labor, but after 6 cm the rate of progression is similar (Obstet. Gynecol. 2012;119:1113-8).
Greater patience with induced labor could reduce the rate of cesarean sections. "These are the women who are getting sectioned," she said.
A separate study suggests that women trying for a vaginal delivery after a prior cesarean section should be assessed by the same progression curves as women without a prior cesarean section (Obstet. Gynecol. 2012;119:732-6).
Clinical variables also have changed since the 1950s in ways that affect the progress of labor. Pregnant women in the United States today are more likely to be obese. A high body mass index prolongs the time it takes for cervical dilation in labor. "We may need a whole new labor curve for these women," Dr. King said.
She reported having no financial disclosures.
On Twitter @sherryboschert