St. Louis Obese women can gain little or no weight during pregnancy - or lose a few pounds - without harming their babies, new research suggests.
Obese mothers who put on less than the recommended 15 pounds were less likely to develop pregnancy-related high blood pressure or deliver by Caesarean section and more likely to have a normal-weight baby, the study showed.
The findings, in the October issue of Obstetrics & Gynecology, fuel growing concern that national weight-gain guidelines for pregnant women are outdated and don't take into account the nation's obesity epidemic.
The Institute of Medicine, which issued the weight guidelines in 1990, is about to consider changing them.
Dr. Raul Artal, one of the study's authors, said the fear has been that not gaining weight would hurt the fetus.
"Not only were there no deleterious effects, but there are benefits," said Artal of Saint Louis University School of Medicine, who supports changing the weight guidelines.
In an accompanying editorial, Dr. Patrick Catalano of Case Western Reserve University, noted that the guidelines were written when the concern was low birth weights. Now it's shifted to rising obesity, he said.
Using information from birth certificates, the study analyzed the pregnancies of more than 120,000 obese women from Missouri to see how weight gain affected their blood pressure, C-sections and the baby's birth weight. Obesity increases a woman's risk of miscarriage and other serious complications.
The study found that 23 percent of the obese women gained less than 15 pounds, 31 percent gained 15 to 25 pounds and nearly half gained more than 25 pounds. Those who gained less had better outcomes.
The researchers considered three levels of obesity based on body mass index, or BMI, and came up with optimal ranges of weight gain. For a BMI of 30-34.9, the best outcomes came with a weight gain of 10 to 25 pounds; gaining less than 9 pounds was best for a BMI of 35-39.9 and losing up to 9 pounds was best for those with a BMI over 40.
The study's strengths are its size - drawing from an entire state - and that it is the first to look at different obesity levels, said Dr. Emily Oken, a Harvard Medical School professor and researcher on obesity, nutrition and weight gain in pregnancy.
The Missouri study found that the least-heavy obese women who lost weight were at somewhat higher risk to have a low birth-weight baby. However, they still benefited by having fewer other complications. Obese women who gain too much are also at risk for low birth-weight babies, Oken said. Artal said that occurs predominantly in obese women with high blood pressure.
Catalano said as almost half of pregnant women gain more than the recommended amount of weight, encouraging them to stay within the current guidelines is a significant challenge. But Artal said he has found women are more likely to modify their behavior during pregnancy because of concern for their child.