Nearly 1 in 4 women now are obese when they become pregnant, according to a new study that includes information from most of the United States.
Researchers analyzed birth certificates from 36 states and Washington D.C. in 2011, which listed how much the mother weighed before she became pregnant.
On average, 23.4 percent of mothers in these states were obese — meaning they had a body mass index (BMI) of 30 or greater — when they became pregnant, according to the report, from the Centers for Disease Control and Prevention.
Utah had the lowest rate of obesity before pregnancy, at 18.0 percent, while South Carolina had the highest, at 28.6 percent. [Obesity before pregnancy: Full list of rates by state]
Mothers were more likely to be obese if they were over age 20, compared with younger mothers. Black and Hispanic women were also more likely to be obese than white women, the report said.
Given the current high rate of obesity in the United States (nearly 36 percent of U.S. adults are obese), it's not surprising that nearly 25 percent of mothers are obese, said Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology at Long Island Jewish Medical Center in New Hyde Park, N.Y., who was not involved in the report. However, Rabin pointed out that the study did not include information from all U.S. states, so it is not representative of the whole population.
Still, "it's important for women to normalize their body weight before they become pregnant," to reduce pregnancy risks for themselves and their babies, Rabin said.
Being overweight or obese during pregnancy is linked with an increased risk of gestational diabetes, cesarean delivery and preeclampsia (high blood pressure) for the mother; as well as prematurity, stillbirth and excessive weight at birth for the fetus, according to the American Congress of Obstetricians and Gynecologists (ACOG).
Rabin said she recommends that women who are already obese when they become pregnant speak with their OB-GYN to make sure they gain the appropriate amount of weight for their health and their baby during pregnancy.
The Institute of Medicine recommends normal-weight women (BMI between 18.5 and 24.9) gain 25 to 35 pounds during pregnancy, and underweight women (BMI of less than 18.5) gain 28 to 40 pounds, but overweight woman (BMI between 25 and 29.9) gain 15 to 25 pounds, and obese women (BMI of 30 and over) gain 11 to 20 pounds.
Women who are overweight or obese during pregnancy should be offered nutrition counseling, and encouraged to follow an exercise program, ACOG says.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.