A new study finds epidurals may make labor longer than doctors initially thought.

Researchers at the University of California, San Francisco found that some women who received epidural anesthesia during labor took up to two hours longer to deliver their child compared to women who didn’t get the shot.  Doctors are initially taught that women who receive an epidural will take about one hour extra to complete the second stage of labor (pushing), however researchers have found that the shot may increase the time of labor from two to three hours.

“The effects of an 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,” said Dr. Yvonne Cheng, the study’s lead author and maternal-fetal medicine specialist at the University of California – San Francisco (UCSF).

Cesarean sections, also known as c-sections, are commonly used when labor has slowed down or if the baby is not progressing naturally through the birth canal.  Today, C-sections are used for about one-third of the baby births in the U.S., about 50 percent more than in the mid 1990s.

The study lead by Cheng compared data from over 42,000 women who delivered children at UCSF between 1976-2008.  Cheng and her team focused specifically on the length of the second stage of labor within the 95th percentile.  This means that 19 out of 20 women would complete the second stage of labor within that time.

The study found that women who had never had children before and were in the 95th percentile took about 3 hours and 20 minutes to complete the second stage of labor with an epidural, as opposed to about 5 hours and 40 minutes for those who didn’t receive the shot.  On the other hand, women who have had children before took about 1 hour and 20 minutes to complete the second stage without an epidural, compared to about 5 hours and 40 minutes for those who did receive an epidural.

Overall, researchers found that the second stage of labor took about two hours longer at the 95th percentile for women who received an epidural.