Close to half of all women who give birth may have problems during their labor and delivery because of weight problems, a new study shows.

Nearly half of all U.S. women of childbearing age are considered overweight or obese. Pregnant women who are overweight or obese progress through labor slower than do normal-weight women, the researchers say.

The report, which appears in the November issue of the journal Obstetrics & Gynecology,was conducted by researchers from the University of North Carolina at Chapel Hill and the National Institute of Child Health and Human Development of the National Institutes of Health.

Anjel Vahratian, PhD, MPH, and colleagues studied data from nearly 600 women aged 16 or older who were each pregnant with one baby. The researchers tracked how long it took for the women to progress through labor, as well as the women’s body mass index (BMI), an indirect measure of body fat.

The scientists defined normal BMI as 19.8-26, overweight BMI as 26.1-29, and obese BMI as greater than 29. That’s close to common standards, which call BMI of 18.5-24.9 normal, BMI of 25-29.9 overweight, and BMI greater than 30 obese.

The study showed that labor took longer in women considered to be overweight or obese.

For women considered to be at a normal weight prior to the delivery, labor lasted on average 6.2 hours. Typically this part of labor can last six or more hours. For overweight women, labor lasted 7.5 hours. Obese women had longer labor lasting almost eight hours.

Long labor is one reason a caesarean (C-section) delivery is done. That may make overweight and obese women more likely to have a C-section.

Obese women have up to a twofold increased risk of C-section during labor compared with normal-weight women, say the researchers, citing previous observational studies.

“An estimated 22 percent of nonpregnant women 18-49 years of age in the United States are considered overweight and an additional 22 percent are classified as obese,” write the researchers.

Ideally, extra weight should be shed before conception. But many pregnancies are unplanned. Since trying to lose weight during pregnancy isn’t a healthy idea, women who aren’t pregnant may fare best by achieving and maintaining a healthy weight, whether they’re trying to get pregnant or not.

The study also has meaning for health care providers, says Vahratian, who was with the University of North Carolina at Chapel Hill when the study was conducted and now works at the University of Michigan at Ann Arbor.

“This finding means that before they recommend a C-section, health care providers need to add to their other considerations a woman’s prepregnancy weight, as well as how much weight she’s gained during the pregnancy,” says Vahratian, in a news release.

By  Miranda Hitti, reviewed by  Brunilda Nazario, MD

SOURCES: Vahratian, A. Obstetrics & Gynecology, November 2004; vol 104. News release, National Institute of Child Health and Human Development, National Institutes of Health. WebMD Health Tools: “Body Mass Index Calculator.”