Women who start out obese need to put on a minimum number of pounds when pregnant, as advised by the Institute of Medicine.
People are considered obese if they have a body mass index, or BMI, of 30 or higher. BMI is calculated on the basis of a person's weight and height. For instance, a 5-foot-4 woman who weighs 174 pounds has a BMI of 30.
In its first new pregnancy weight guidelines in 19 years, the Institute of Medicine (IOM) in May advised obese moms-to-be to gain 11 to 20 pounds.
But even that might be too much, says obstetrician/gynecologist Kim Vesco, director of the upcoming "Healthy Moms" clinical trial of weight control during pregnancy.
Some studies have suggested that little or no weight gain "is actually associated with better outcomes for obese women," says Vesco of the Kaiser Permanente Center for Health Research in Portland, Ore. Excess pregnancy weight raises the risk of pregnancy-induced hypertension and diabetes, C-sections and birth injuries.
The government-funded "Healthy Moms" study will begin enrolling 180 obese pregnant women this month in Washington state and Oregon. They'll be randomly split into two groups: One will get an individual counseling session on diet and exercise, and the other will get two such sessions, followed by weekly group counseling for the rest of their pregnancy.
The researchers will make sure that the women are eating enough and not feeling hungry and that their fetuses are growing well, Vesco says.
The group sessions, a first for pregnant women, will seem familiar to Weight Watchers members. "It's that concept of accountability," Vesco says, citing the weigh-ins, the food and exercise diaries and the group support.
U.S. World and News Report has contributed to the report.