First-time mothers who have their labor induced may face a greater risk of needing a cesarean section than those who go into labor naturally, a new study finds.

In a study of 7,800 first-time mothers who gave birth at one U.S. medical center, researchers found that those who had their labor induced were twice as likely to ultimately need a C-section.

Of all women in the study, 44 percent had their labor induced - and the researchers estimate that failed induction accounted for 20 percent of the C-sections performed.

The findings, reported in the journal Obstetrics & Gynecology, firm up the link seen in past studies between labor induction and an increased risk of C-section. By definition, labor induction is performed before a woman’s body is ready for spontaneous labor, and in some cases there will be problems with labor progression that necessitate a C-section.

The connection is important because while cesarean section is a generally safe procedure, it requires a longer recovery time than vaginal birth, and does present certain risks, such as blood clots, infection at the incision site or in the lining of the uterus, and breathing problems in the baby.

Moreover, the rates of both labor induction and C-section have been on an upward trend in the U.S. since the 1990s. Labor inductions have risen from just under 10 percent of births in 1990 to 22 percent in 2006; and in 2007, C-sections were done in almost one-third of all births.

The current findings suggest that putting more limits on so-called “elective” inductions would help lower the number of C-sections performed nationally, according to lead researcher Dr. Deborah B. Ehrenthal of the Christiana Care Health System in Newark, Delaware.

There are circumstances in which labor induction may be advisable. There is good evidence, for example, that inducing labor benefits mom and baby when pregnancy goes beyond 41 weeks, Ehrenthal told Reuters Health in an interview.

Normally, pregnancy lasts about 40 weeks, and prolonged or “post-term” pregnancy carries an increased risk of certain complications, including stillbirth.

According to the American College of Obstetrics and Gynecology (ACOG), labor induction may also be warranted in certain other circumstances - such as when a mother has pregnancy-related high blood pressure or diabetes, or when the mother’s “water breaks” but labor does not spontaneously begin.

In general, elective labor induction refers to those done with no clear medical reason. It may be done for convenience, for example, or in cases where late pregnancy is causing significant physical discomfort or when a woman wants to ensure that her own doctor delivers the baby.

Of the labor inductions performed in this study, 40 percent were elective. The findings were based on women’s medical records, and Ehrenthal said that her team considered any induction without a documented maternal or fetal indication to be elective. The precise reasons for those elective inductions are unknown.

It is not possible to tell what the “right” number of labor inductions in this study group - or among pregnant women in general - should be, according to Ehrenthal. “Were we doing the right number 15 years ago, or are we doing the right number now? We don’t know,” she said.

According to Ehrenthal, the bottom line for pregnant women is that they should understand the reasons for and potential risks of all forms of delivery. “It’s really important to have a frank discussion with your doctor about all of your options for delivery,” she said.

Dr. Caroline Signore, a scientist with the U.S. National Institute of Child Health and Human Development who wrote an editorial published with the study, agreed that women contemplating an elective labor induction should be aware of the relatively higher risk of C-section.

In an interview, she also pointed out that when first-time moms have a C- section, they often have repeat cesareans with any future pregnancies. So limiting the need for C-section in first-time pregnancies is particularly important.

Signore said that the rate of labor induction in this study - at 44 percent - was striking.

Even among the 4,600 women in the study considered “low risk” for needing a labor induction - because they were not post-term, were free of diabetes, high blood pressure and obesity, and the fetus was not overly large - 29 percent had their labor induced. (The portion of those that were elective was not reported.)

Among these low-risk women, one-quarter of those who had a labor induction ended up needing a C-section, versus 14 percent of those who had a natural labor.

According to Signore, it is not clear why national rates of labor induction - and elective labor induction in particular - have risen so significantly since the 1990s.

But the current findings, she said, underscore a widespread need for medical centers and providers to try to cut rates of “inappropriate” labor induction. “Labor induction performed for no medical reason is an area for us to target,” Signore said.

In her editorial, Signore also points out that according to ACOG guidelines, elective inductions and elective C-sections should not be scheduled before the 39th week of pregnancy, in order to reduce the odds of complications associated with relatively earlier birth.

However, she adds, recent studies suggest that this guideline is “not followed rigorously.”

A study published last month, for example, found that as the U.S. national rate of labor induction rose between 1992 and 2003, so did the proportion of births occurring at the earlier end of full-term - that is, in the 37th or 38th week.

In 2003, the study found 30 percent of all full-term singleton births occurred during the 37th or 38th week, versus 19 percent in 1992. The researchers concluded that labor inductions performed before the 39th week were a “likely cause” of that trend.

SOURCE:  Obstetrics & Gynecology, July 2010.