Obese Women Retain More Pregnancy Weight

Oct. 21, 2009 -- Gaining no weight during pregnancy or even losing a little weight may be healthier for obese women and their babies than gaining too much weight.

In research made public today, the investigators from Kaiser Permanente confirmed that obese women who gain more weight than they should during pregnancy are more likely to keep the weight on.

Nearly three out of four women in the study gained more than 15 pounds during pregnancy, and, on average, these women retained 40% of the extra weight a full year after giving birth.

"Younger women and first-time mothers were the most likely to gain too much weight," obstetrician/gynecologist and study lead author Kimberly K. Vesco, MD, tells WebMD. "The extra weight increased the risk for complications like hypertension, diabetes, preeclampsia, C-sections, and birth injuries."

Half of Pregnant Women Overweight

Nearly half of pregnant women in the United States today are either overweight or obese -- up from about 25% four decades ago.

Obesity is defined as having a body mass index (BMI) of 30 or more, and for most women that means carrying at least 30 extra pounds. A BMI of 18.5-24.9 is considered normal weight, and 25-29.9 is considered overweight.

For example, a 5-foot, 2-inch-tall woman who weighs 135 pounds would be considered at the upper limit of the normal range (BMI = 25), and she would be considered obese at 165 pounds (BMI = 30).

A 5-foot, 7-inch woman would be considered normal weight up to 160 pounds (BMI = 25) and obese at 195 (BMI = 30).

The independent health policy group Institute of Medicine now recommends that normal-weight women gain between 25 and 35 pounds during pregnancy, overweight women gain 15 to 25 pounds, and that obese women gain between 11 and 20 pounds.

A total of 1,656 women with BMIs of 30 or more at the start of their pregnancies were enrolled in the newly published study. The women were followed for up to 18 months after delivery.

Putting Pregnant Women on a Diet

Some studies suggest that babies born to obese women who don't gain much weight during pregnancy have fewer delivery complications and better outcomes than babies born to women who gain more weight than is recommended.

The Kaiser researchers recently began recruitment for a study examining whether very obese women and their babies fare even better when they gain no weight at all.

The "Healthy Moms" study, funded by a $2.2 million grant from the federal government, will include women who are 50 to 100 pounds above their normal weight at the start of pregnancy, Kaiser Permanente Center for Health Research senior investigator Victor Stevens, PhD, tells WebMD.

"These are not women with just a few pounds to lose," he says. "These are women who are carrying so much extra weight that it is a risk to themselves and their baby."