Aug. 21 (UPI) -- More than 60% of babies who die in infancy are born to mothers who were overweight or obese prior to becoming pregnant, according to figures released Friday by the U.S. Centers for Disease Control and Prevention.
The infant mortality rate for babies born to overweight women in the United States in 2017-18 was 5.2 for every 1,000 births, while it was 7.1 for every 1,000 births for women who were obese, the data showed.
The mortality rate for babies delivered by obese mothers was 55% higher than the rate for women of normal weight, which was 4.6 per 1,000 births, the agency said.
"Infants born to women who were normal weight before pregnancy generally had lower mortality rates compared with infants born to women who were underweight, overweight and with obesity," the CDC researchers wrote.
Just over one-half of women who gave birth in the United States in 2018 were overweight or had obesity before becoming pregnant, according to CDC estimates.
Obesity during pregnancy has been linked to complications and, for babies, increased risk for gestational diabetes, pre-eclampsia, eclampsia and death, the agency said.
The findings are based on National Center for Health Statistics' calculations of mothers' pre-pregnancy body-mass index, or BMI, which is calculated by taking the mother's weight before pregnancy divided by the mother's height in inches squared and multiplying that figure by 703.
Women with a pre-pregnancy BMI less than 18.5 were considered underweight, while those with BMI of 18.5 to 25 were defined as normal weight, the agency researchers said.
Mothers were considered overweight if their pre-pregnancy BMI was between 25 and 30, and they were defined as obese if it was above 30, according to the researchers.
They analyzed data for 99.6% of the 22,341 infant deaths among U.S. residents in 2017 and 99.3% of the 21,498 infant deaths in 2018, they said.
Among infants who died, 3.5% were born to women who were underweight and 35.8% were born to women of normal weight, the CDC said.
Roughly 61% of infants who died in 2017 and 2018 were born to women who were overweight -- 25% -- or had obesity -- 36% -- prior to becoming pregnant, the data showed.
Infant mortality rates were higher for babies born to Black mothers of normal pre-pregnancy weight -- 9.1 per 1,000 births -- and those with obesity -- 12 per 1,000 births -- than for White and Hispanic mothers, according to the CDC.
For White mothers, infant mortality rates were 4.2 per 1,000 births for those with normal pre-pregnancy weights and 5.7 per 1,000 births for those with obesity, the data showed.
For Hispanic mothers, these figures were 4.3 and 5.7 per 1,000 births, respectively, the CDC said.
"Generally, infant mortality increased as maternal BMI increased from the normal through obese weight categories," the agency researchers wrote.