How Pregnancy Weight Gain Could Contribute to the Obesity Epidemic

Putting on too many pounds during pregnancy can affect your child's health for life.


You've heard plenty about the childhood obesity epidemic. What you may not know is that moms-to-be are contributing to the problem. When women weigh too much at conception or gain too much during pregnancy, they can set their children on the path to obesity and add to the next generation's weight struggles.

As it is, nearly half of U.S. women enter pregnancy overweight, one-fifth are obese when they conceive and up to 40 percent of all pregnant americans gain more than recommended. This excess weight is hard on moms. Studies have shown that being overweight or obese is associated with gestational diabetes, high blood pressure, premature labor and newborns larger than 8 pounds, 13 ounces, a size more likely to cause birth injuries. Heavy women also have longer labors, one reason they're at higher risk for cesarean section. But the most provocative new research is looking at the impact of a mom's extra pounds on her baby. Here are some of the latest findings:

Bigger isn't better

When a mom-to-be weighs too much, her body becomes an "obesogenic environment," says Yuan-Xiang Pan, Ph.D., a professor of molecular nutrition at the University of Illinois at Urbana-Champaign. He compared normal-weight and obese rats during pregnancy and found the heavier moms had more harmful fats in their blood and more of a hormone that lowers sensitivity to hunger cues. For their fetuses, this was like growing up in a neighborhood full of fast-food restaurants: Unhealthy nutrition was programming them to become obese.

It's long been clear that heavy moms risk having babies with abnormally high birth weight—often a result of the mother's elevated blood sugar or gestational diabetes—but a new study found that mom's extra weight can alter the baby's body composition.

"When pregnant women gain too much, their newborns are significantly fatter," says Jami Josefson, M.D., a pediatric endocrinologist at the Ann & Robert H. Lurie Children's Hospital of Chicago, who used innovative methods to measure the body fat of newborns. Even when the mom had healthy blood sugar levels and birth weight was normal, these infants averaged 17.5 ounces of body fat compared with just 13.9 ounces in the leaner newborns whose moms had gained a healthy amount of weight. A high birth weight raises the risk for childhood obesity, Josefson says, but extra fat at birth could be an additional risk factor.

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Fallout from mom's weight may linger beyond childhood, say Israeli researchers who looked at clinical information on 1,400 young adults born between 1974 and 1976, including data on their mothers' weight before pregnancy. By age 32, those whose mothers' prepregnancy weight was in the upper 25 percent had higher risks for heart and metabolic disease than those with moms in the lowest 25 percent. Their waists averaged 3.3 inches larger, their BMI averaged five points higher, and they had significantly higher blood pressure and blood levels of sugar and fat.

Paradoxically, dieting at the time of conception could also be problematic. An animal study found that eating too little at the start of pregnancy altered DNA in a part of the fetal brain related to food and blood sugar, which boosted the offspring's risk of being overweight later in life.

What to do

Already-heavy women are the most likely to gain excess pregnancy weight—Josefson's study found a 70 percent likelihood!—but about one-third of normal-weight women also gain too much. Aside from postponing pregnancy until your weight is normal, the best thing you can do for your baby is eat right while you're expecting. A review of 44 studies found that expectant moms who ate a balanced, healthy diet gained an average of 9 fewer pounds than those who ate as usual. In contrast, moms-to-be who exercised but ate their usual diet gained just 1.5 fewer pounds.

Even dieting is gaining acceptance, though only for obese women who have their doctor's OK. A balanced diet that enables them to gain little or no weight during pregnancy is not only safe for the baby, it can help prevent preeclampsia, diabetes, high blood pressure and premature birth.

Obesity and your baby's brain

Scientists have discovered that a mother's weight can alter the delivery of nutrients to the fetal brain. One study showed that obese moms risked delivering babies with low iron reserves, perhaps because obesity promotes production of the hormone hepcidin, which may interfere with the transfer of iron to the fetus. Iron is crucial to the central nervous system; deficiency puts babies at risk for delays in motor and cognitive development.

Other research found that the children of moms who were obese before pregnancy tested two points lower in math and three points lower in reading at ages 5 and 7. The differences seem slight, but they correlate with seven fewer years in a mother's education and significantly lower household income, both classic risk factors for low test scores.