These “ideal” women had a preterm birth rate of 7.6 percent, according to DeFranco, who is also an associate professor of maternal-fetal medicine at the University of Cincinnati College of Medicine.
Women who had less than a year between pregnancies as well as those who gained too little weight during pregnancy had higher rates of preterm births, the study authors said.
The highest rate of preterm births — at 25 percent, more than triple that of the ideal group — occurred among women who were underweight when they got pregnant, had shorter gaps between pregnancies and inadequate weight gain during pregnancy, the researchers reported.
Women who are underweight are advised to gain 28 to 40 pounds during pregnancy, while normal weight women should aim for 25 to 35 pounds, according to Institute of Medicine recommendations. Overweight women should gain 15 to 25 pounds, and those who are obese should only gain 11 to 20 pounds.
A body mass index (BMI) between 18.5 and 24.9 is considered a healthy weight. BMI is an estimate of body fat based on height and weight.
“You have some control over your risk of a preterm birth,” DeFranco said, urging women to pay attention to the factors they can adjust. Other risks are not changeable. For instance, black women are more likely to have preterm births, as are women who have had a previous one and those who conceive through in vitro fertilization, the researchers said.
Dr. David Mendez, a neonatologist at Nicklaus Children’s Hospital in Miami, reviewed the study. He pointed out that the findings build on some things that doctors have suspected.
“It does appear to show that the uterus needs some recovery time, and the mom needs to be at a healthy weight to have the best outcome,” he said. Paying attention to the recommended weight gain is also important, he added.
For women who are trying to conceive, Mendez said, the message seems to be to try to get to a healthy weight ahead of time.
The findings were published online recently in the Maternal and Child Health Journal.
SOURCES: Emily DeFranco, D.O., associate professor, maternal-fetal medicine, University of Cincinnati College of Medicine, and researcher, Center for Prevention of Preterm Birth, Cincinnati Children’s Hospital; David Mendez, M.D., neonatologist, Nicklaus Children’s Hospital, Miami; Aug. 3, 2016, Maternal and Child Health Journal, online