Pregnant women who are overweight or obese progress through labor more slowly than do normal weight women, according to a study by researchers at the University of North Carolina and the National Institute of Child Health and Human Development of the National Institutes of Health.
Since a longer labor is one consideration for whether or not a pregnant woman will have a Caesarean section, the new finding also means that a physician may need to take a woman's weight into account before deciding whether or not to recommend her for the procedure, the study authors caution.
The study appears in the November issue of Obstetrics and Gynecology.
When taken together with other findings showing that extra body weight during pregnancy can pose serious and even life-threatening complications for both mother and infant, the current finding underscores the need for overweight or obese women who are either pregnant or contemplating pregnancy to seek medical attention.
"An overweight or obese woman contemplating pregnancy should speak with her physician about a diet and exercise program to help attain a healthy weight before she gets pregnant," said Duane Alexander, M.D., Director of the NICHD. "A pregnant woman who is overweight or obese should speak to her physician about a diet and exercise program to help ensure the nutritional needs of her developing fetus."
Overweight and obesity have long been known to complicate pregnancy. Both overweight and obesity increase the chances for such serious and potentially life-threatening complications of pregnancy as gestational diabetes, pregnancy-associated hypertension, and preeclampsia.
In the current study, researchers analyzed pregnancy and birth records from 612 North Carolina women who gave birth to their first child. The researchers undertook the study to determine why obese and overweight women are more likely to have a caesarean section.
The increase in labor duration among overweight and obese women accounts, in part, for their increased C-section rate, said the study's first author, Anjel Vahratian, Ph.D., M.P.H, who conducted the analysis while on a research training fellowship in NICHD's Division of Epidemiology, Statistics, and Prevention Research. The analysis was undertaken while Dr. Vahratian was a doctoral candidate at the University of North Carolina at Chapel Hill.
Dr. Vahratian explained that the decision on whether or not a pregnant woman should deliver by C-section is extremely complicated. Attending physicians need to consider a variety of factors before making the decision, such as how rapidly labor progresses, as well as any complications of pregnancy.
"Nearly one-half of the women of childbearing age are either overweight or obese," Dr. Vahratian said. "This finding means that before they recommend a C-section, health care providers need to add to their other considerations a woman's pre-pregnancy weight, as well as how much weight she's gained during the pregnancy."
To determine whether the women qualified as either obese or overweight, the researchers relied on body mass index (BMI) standards for pregnancy developed by the Institute of Medicine. BMI is calculated by dividing body weight, in Kilograms, by a woman's height, in meters, squared. Women with a body mass index of from 19.8 to 26 were defined as normal, from 26.1 to 29 as overweight, and above 29 as obese. When using equivalents in pounds, feet, and inches, a 5 foot, 4 inch woman weighing 152 pounds would have a BMI of 26, while 5 foot, 4 inch woman weighing a 169 pounds would have a BMI of 29.
The researchers found that, for both overweight and obese women, the active duration of labor took longer than it did for normal weight women. Active labor is the part of labor in which the cervix opens so the fetus can move through the birth canal. Specifically, the researchers recorded the time it took for a woman's cervix to dilate from 4 centimeters to 10 centimeters.
The researchers found that the median labor for overweight women was 7.5 hours, for obese women 7.9 hours, and for normal weight women, 6.2 hours. The "median" is a statistical term used to classify items in a series. In a ranking of 1 to 100, the median is the ranking that falls at 50.
Dr. Vahratian cautioned women about beginning a weight loss program without medical advice. Many fad diets, she said, might result in some weight loss, but at the expense of good nutrition. Although her advice applies to women who are not yet pregnant, it is especially important for women who are already pregnant.
"About half of all pregnancies are unplanned," Dr. Vahratian said. "It's crucial for a pregnant woman to obtain early prenatal care, in order to work out a nutritional plan with her doctor, to make sure that she's getting adequate nutrition for herself and her developing fetus."
Dr. Vahratian is now at the University of Michigan at Ann Arbor. Other authors of the study were Jun Zhang, M.D., Ph.D., James Troendle, Ph.D., both of NICHD's Division of Epidemiology, Statistics, and Prevention Research and David Savitz, Ph.D. and Anna Maria Siega-Riz, Ph.D., both of the University of North Carolina at Chapel Hill and the Carolina Population Center.
The NICHD is part of the National Institutes of Health (NIH), the biomedical research arm of the federal government. NIH is an agency of the U.S. Department of Health and Human Services. The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. NICHD publications, as well as information about the Institute, are available from the NICHD Web site, http://www.nichd.nih.gov, or from the NICHD Information Resource Center, 1-800-370-2943; e-mail NICHDInformationResourceCenter@mail.nih.gov.