TUESDAY, June 22 (HealthDay News) -- Inducing labor more than doubles the risk of having a cesarean delivery, according to a new study that puts some hard-and-fast numbers to a link that experts have long suspected.

"Induction of labor doubles the risk of C-section," said study author Dr. Deborah Ehrenthal, director of women's health programs at Christiana Care Health System in Newark, Del., and an assistant professor of family medicine at Jefferson Medical College of Thomas Jefferson University in Philadelphia. The research appears in the July issue of Obstetrics & Gynecology.

Many decisions to induce labor are medically necessary, including situations in which it's deemed safer to deliver the baby than to continue the pregnancy. But many inductions are "elective," requested typically by a woman or her doctor, Ehrenthal also found in her study. "There are concerns that deliveries are being scheduled [and labor-induced] for non-medical reasons."

Among them, she said, are women electing to have labor induced when their partner is available, such as being back in town from a business trip.

"We need to understand it's not without risk to be doing this," Ehrenthal said of some elective inductions and the higher risk of C-sections. "There are significant risk to moms for C-sections."

In her study, Ehrenthal focused on 7,804 women giving birth for the first time who delivered single infants at term, between 37 and 42 weeks.

She found that labor was induced in 43.6 percent of the women, and 39.9 percent of those were elective inductions.

Then Ehrenthal looked at the women who had C-sections and found that use of labor induction (whether elective or not) increased the odds of having a C-section by more than 2.6 times.

Put another way, "20 percent of the cesareans were attributed to the induction, whether elective or not," Ehrenthal said. "We need to be a little bit less ready to do an induction."

Of the 43.6 percent of women induced, she said, "it's a very high rate of induction."

Inductions have been rising, said Dr. Caroline Signore, an obstetrician-gynecologist at the Eunice Kennedy Shriver National Institute of Child Health and Human Development at the U.S. National Institutes of Health, who wrote an accompanying commentary.

In 1990, just 9.5 percent of U.S. women had labor induced, she wrote, but it was 22.5 percent by 2006.

The new study, she said, puts a number on what experts suspected -- that the rise in induced labors is driving the rise in C-sections -- now at an all-time high of 32 percent of deliveries in the United States.

Elective inductions should not be done before 39 weeks' gestation, according to recommendations by the American College of Obstetricians and Gynecologists, but that guideline is not rigorously followed, Signore noted. In the study, some of the women were induced as early as 37 weeks.

In 37 percent of the women induced, the women's cervix was not sufficiently ready, Ehrenthal found.

Having one C-section also increases the chances of having to have a C-section in later deliveries. "Emerging evidence shows increasing risk with increasing cesarean deliveries. Preventing the primary C-section can stop that cascade," and reducing elective labor inductions is one way to do that, she said.

More information

To learn more about labor induction, visit the March of Dimes.