While a shot to relieve labor pains is known to increase the time it takes for women to deliver babies, a new study says the increase may be longer than originally thought.
Researchers found some women who received epidural anesthesia during labor took more than two hours longer to deliver their child, compared to women who didn't get the pain reliever.
"The effect of epidural can be longer than we think and as long as the baby looks good and the women are making progress, we don't necessarily have to intervene (and perform a Cesarean section) based on the passage of time," Dr. Yvonne Cheng told Reuters Health.
She is the study's lead author and a specialist in maternal-fetal medicine at the University of California, San Francisco.
Cesarean sections, or c-sections, are now used for about one of every three births in the U.S., according to the Centers for Disease Control and Prevention. That's about 50 percent more than in the mid-1990s.
C-sections come with longer hospital stays and extra risks for mothers and babies.
Cheng and her colleagues write in Obstetrics and Gynecology that two common reasons for performing c-sections are that it appears labor has slowed and that the baby is not progressing through the birth canal.
Traditionally, doctors are taught that women who receive epidural anesthesia will take about an extra hour to complete the second stage of labor, which is the pushing part.
But the researchers write that it's unclear where the data for what's considered a "normal" labor came from and that the extra hour of labor is an average.
For the new study, they compared data from over 42,000 women who delivered their children at the University of California, San Francisco between 1976 and 2008. About half of the women received epidural anesthesia and the other half did not.
Specifically, the researchers were looking at the length of the second stage of labor at the 95th percentile, which is an extreme. That means 19 out of 20 women would complete that stage of labor within that time.
For women who had never had a child before and were in the 95th percentile for length of labor, the second stage took about three hours and 20 minutes to complete without anesthesia and five hours and 40 minutes with the shot.
Women who previously had a child, who usually have shorter labors to begin with, took about an hour and 20 minutes to complete the second stage of labor without anesthesia at the 95th percentile. That compared to four hours and 15 minutes with an epidural.
Overall, the researchers found the second stage of labor took about two hours longer at the 95th percentile when women got an epidural.
For women who have a more typical delivery, the epidural probably adds less time, Dr. Karin Fox said. "It's probably difficult to know for each individual patient," she told Reuters Health.
While she said the results are not surprising, there may be reasons besides the epidural why some women's labors last longer.
Dr. Christopher Glantz cautioned that although the health of babies in the epidural and non-epidural groups was similar, mothers tended to have more complications if they had longer labors.
Glantz was not involved with the study but is a high-risk pregnancy specialist at the University of Rochester Medical Center in New York.
"It would appear that the upper limit of what can be tolerated is greater than what was previously thought, which takes away some of the impetus to intervene (with c-section) in what appears to be a premature fashion," he said.
Cheng and her colleagues write that while doctors should not only rely on this paper to establish how long labors may last, these findings and previous research suggest current definitions are not sufficient.
"All the experts in the field should get together to look at the evidence that's out there and come up with informed definitions," Cheng said.