Can Pregnancy Weight Gain Cause Child Obesity?

Every pregnant woman knows she's eating for two. But if she indulges too much during the nine months she's carrying her baby, she could be creating serious weight-loss problems for two, as well.

That's the latest theory among researchers trying to unravel the mystery of the childhood-obesity epidemic. Though the startling three-decade rise in childhood obesity appears to have leveled off, according to a new study published in this week's issue of the Journal of the American Medical Association, researchers say the rate is still way too high: more than three times that of the 1970s. Doctors have long known that children's lifestyle habits—how much they eat and exercise—play a role in determining whether they gain too much weight. But the role of genetics has been less clear, says Dr. Thomas M. Badger of the USDA-Arkansas Children's Nutrition Center. Some data seem pretty straightforward: bigger moms tend to give birth to bigger newborns, who often become heavier than normal children and prove to be at high risk for becoming obese adults. These correlations seem to suggest that much of obesity is genetically predestined.

Overweight women don't always produce overweight kids, but researchers noticed that kids were much more likely to have weight problems if they had an overweight mother than a heavy dad. They wondered if excessive weight gain before or during pregnancy might directly affect the metabolic programming of the developing fetus. In other words, could an overweight pregnant woman be creating an environment inside her uterus that predisposed her child to put on fat more quickly than the offspring of normal-weight mothers, even when both groups of babies ate similar foods and got the same level of exercise?

To begin to answer this question, the Children's Nutrition Center completed a study, published early this year in the American Journal of Physiology, in which they overfed one group of normal-sized female rats (to eliminate the possibility of inheritance of obese genetic influences) before mating them with lean males. A second group of normal-sized females was fed a healthy diet before being mated with similarly sized males. After all the pups were born and weaned, both groups were fed a high-fat diet. After 130 days on the diet, the offspring of the obese females were four times heavier and put on 60 percent more subcutaneous and abdominal fat, even though the calorie intake of both groups was the same.

"They were programmed differently, so they responded differently," says Badger. "We think there's a high likelihood that something similar is happening in humans, in terms of programming kids to become overweight later in life."

However, that doesn't mean that everyone who is obese is metabolically programmed in utero, he says. The issue of why children become obese and overweight is "very complex," and there isn't a single explanation. But researchers want to identify who might be affected and understand the mechanism involved so they can help prevent mothers from unwittingly predisposing their unborn children to putting on fat more quickly. (Once a child is older, Badger says, obesity is much more difficult to reverse.)

Inspired by their initial results, Badger's team is now focused on getting a follow-up study of human mothers-to-be and their children under way. In the meantime, Badger says women considering pregnancy should use these early results to motivate themselves to get into the best health possible before conceiving. "We'd recommend that women try to lose weight and increase their activity levels, and that their doctors should work with them on this prenatally," he says. "It's the rare mother who doesn't really want to do the right thing, if [she] understands what the consequences are and can take action to prevent it."

That advice can't be taken soon enough, says Anna Maria Siega-Riz, a public-health expert at the department of epidemiology and nutrition at the University of North Carolina School-Chapel Hill. Not only are too many women overweight before they get conceive, but studies indicate that most pregnant women—whether they started out normal-sized, overweight or obese—are gaining more weight during their nine months than the national guidelines currently recommend.

"Physicians are doing a poor job informing women how much they should gain during pregnancy," says Siega-Riz. "Most women are not aware of the existing guidelines or don't understand them." Pregnant women are all encouraged to gain weight during their pregnancies, but the specific amount should be tailored to the woman's height, build and preconception weight, she said. For example, underweight moms are encouraged to gain 28 to 40 pounds, normal-weight moms should gain 25 to 30 pounds, overweight women 15 to 20 pounds and obese moms at least 15 pounds. But a study done at UNC revealed that 60 percent of normal-weight moms, 80 percent of overweight moms and 75 percent of obese moms gained excessive amounts of weight during their pregnancies, while only 35 percent of underweight women gained more than they were supposed to.

To many women, "eating for two" implies doubling your intake, but in fact, Siega-Riz says, a pregnant woman only needs to add the equivalent of one healthy snack, such as a glass of milk and a peanut butter sandwich on whole wheat, to her daily pre-pregnancy diet. Siega-Riz says more doctors need to initiate the conversation about fitness and pregnancy before their patients conceive: "We've done a disservice to pregnant women because we wait too long to get them in good condition, and once they are pregnant, we don't do enough to support them."

In addition to concerns about childhood obesity, she adds, extra weight during pregnancy increases the risk of complications for both mother (higher rates of gestational diabetes, pre-eclampsia, and cesarean births) and child (increased risk of birth defects). Maternal obesity, says Siega-Riz, is now considered the "No. 1 problem facing prenatal-care providers in the new millennium."

Still, Badger says he is optimistic that the situation can be turned around. As they were preparing their rat study for publication, one of the women in his office was so influenced by their results that she decided to put off trying to get pregnant until she lost weight, improved her diet and began exercising more regularly. "She wanted a child in the worst way, but she decided to get on the ball, and she got into better shape before she got pregnant," he says. "We think that if more people could alter their behavior in the same way, they could save themselves and their children a lot of heartache." Or to put it differently, pounds of prevention could be worth many more pounds of cure.