How ONE IN FOUR women are obese when they become pregnant Nearly one in four women in the U.S. are obese when they become pregnant. According to a new study by the Centers for Disease Control and Prevention, 23.4per cent of mothers in the country had a body mass index of at least 30 when they became pregnant. Not only does a woman's obesity pose health risks to herself during childbirth, but it also increases the baby's chance of being born premature, excessively heavy or stillborn. Scary statistic: According to a new study by the Centers for Disease Control and Prevention, 23.4per cent of mothers in the country had a body mass index of at least 30 when they became pregnant The study looked at birth certificates from 2011 in 36 states and Washington, D.C., which listed the mother's weight before she became pregnant. Of the states that were analyzed, Utah had the lowest rate of obesity before pregnancy, at 18per cent. Also far down on the list was Colorado, which had an 18.8per cent rate of obesity before pregnancy. The state with the highest rate - at 28.6per cent - was South Carolina, followed by North Dakota, Wisconsin and Kentucky. The analysis also found that mothers were more likely to be obese if they were over 20 years old, and that black and Hispanic women have a higher rate of obesity than white women. While a woman is expected to gain weight during pregnancy, putting on too much when you are overweight to begin with can pose health risks, says Dr Jill Rabin, chief of ambulatory care, obstetrics and gynecology at Long Island Jewish Medical Center in New Hyde Park, New York. Indeed, being overweight or obese while pregnant has been linked to a higher risk of gestational diabetes, cesarean delivery and preeclampsia. 'It's important for women to normalize their body weight before they become pregnant' A such, 'it's important for women to normalize their body weight before they become pregnant,' says Dr Rabin. According to the Institute of Medicine, women with a normal BMI of between 18.5 and 24.9 should gain between 25 and 35lbs during pregnancy, and those with a low BMI of under 18.5., which is considered underweight, should put on 28 to 40lbs. Overweight women (with a BMI of between 25 and 29.9) should gain 15 to 25lbs, and obese women with a BMI of at least 30 should only gain between 11 and 20lbs during pregnancy. Currently, nearly 36per cent of all adults in the U.S. are considered obese. South Carolina: 28.6% North Dakota: 28.5% Wisconsin: 27.8% Kentucky: 27.4% Georgia: 27.3% Louisiana: 27.2% Michigan: 25.9% Indiana: 25.7% Oklahoma: 25.4% Ohio: 24.8% New Mexico: 24.8% Iowa: 24.8% Washington: 24.7% Delaware: 24.7% North Carolina: 24.4% Missouri: 24.4% Tennessee: 24.3% Illinois: 24.1% Maryland: 23.7% Kansas: 23.7% Nebraska: 23.5% Oregon: 23.4% Texas: 23.3% Vermont: 23.2% South Dakota: 23.2% Pennsylvania: 22.9% Montana: 22.9% New Hampshire: 22.6% Wyoming: 22.1% Florida: 21.8% Idaho: 21.7% California: 21.6% Nevada: 21.1% New York: 20.4% District of Columbia: 20.3% Colorado: 18.8% Utah: 18.0%