Labor Takes Longer For Overweight and Obese Women, Study Finds
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,
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.