A long-standing “rule” for women in labor has been challenged again.
During labor, the cervix – the narrow, lower part of the uterus – dilates, or opens, to allow for a baby’s birth. For decades, the guidance has been that the cervix should dilate by at least 1 centimeter per hour. But a study in two African countries found a slower rate of dilation for many women who went on to have healthy, vaginal births, researchers report online January 16 in PLOS Medicine.
The new study reinforces findings from recent research on pregnant women in the United States, Japan and other countries. Nevertheless, some doctors still wrongly classify slower labor as abnormal, researchers say, leading to unnecessary, potentially risky interventions such as cesarean delivery.
“It takes repetitive studies and consistent findings to change long-held beliefs,” says Aaron Caughey, a maternal-fetal specialist at Oregon Health & Science University in Portland, who was not involved in the study. “Clinicians need to understand there is great variability in labor length.”
For the latest study, Olufemi Oladapo, a medical officer in the department of reproductive health and research at the World Health Organization, and colleagues gathered data on more than 5,500 laboring women admitted to 13 hospitals in Nigeria and Uganda. All of the women had gone into labor naturally, had been pregnant with single babies positioned head-first, and had healthy, vaginal births.
For both first-time mothers and those who had given birth previously, it often took longer than one hour for the cervix to dilate by 1 centimeter. Overall, dilation was slower until the cervix had expanded to 5 centimeters, after which it progressed more quickly. Individual labor times varied. Some first-time mothers had their cervix expand from 4 to 5 centimeters within two hours; for others, it took up to seven hours.
“There are several aspects to labor progression, and cervical dilation is just one of them,” says Oladapo. As long as the vital signs of the mother and baby are fine and the baby’s head is descending, a dilation rate of less than 1 centimeter per hour is not a sufficient reason to intervene, he says. Instead, clinicians should support the laboring woman by providing food, drink, pain relief and the freedom to move and find a position in which she is comfortable, he says.
A 2014 report on preventing unnecessary cesarean deliveries gives similar advice. Coauthored by Caughey, the report called for changing how abnormally progressing labor is defined due to new evidence of longer labors in U.S. women. C-sections come with a higher risk of maternal death and complications than vaginal delivery. Yet about one in four first-time pregnancies considered low-risk, with a single baby positioned head-first, still resulted in a C-section in the United States in 2015, according to the Centers for Disease Control and Prevention.
The cesarean delivery rate has declined slightly among these women, from 26 percent in 2014 to 25.8 percent in 2015. “My sense is that there have been some changes” in how physicians approach the progression of labor, Caughey says. “But I think there is still great heterogeneity in practice in the U.S.”