June 7, 2011 -- Women who put on too much weight during their pregnancy are more likely to give birth to newborns with excessive body fat, and this may set their children up for being overweight or obese as they age, a study suggests.
The new findings, which were presented at the Endocrine Society's 93rd Annual Meeting in Boston, held even if the mother was normal weight before becoming pregnant.
"Excessive weight gain during pregnancy is certainly a factor that contributes to the childhood obesity epidemic, but it's just one factor," says study researcher Jami Josefson, MD, a pediatric endocrinologist at Chicago's Children's Memorial Hospital and assistant professor at Northwestern University Feinberg School of Medicine.
Previous studies have found similar associations between maternal weight gain and newborns with body fat, but these studies did not control for the mom's diabetes status during her pregnancy. Women with gestational diabetes often give birth to larger babies. The new study evaluated pregnant women without gestational diabetes.
Excessive Weight Gain in Pregnancy
Of 56 mothers, 31 women adhered to the recommended guidelines for healthy pregnancy weight gain, and 25 exceeded these guidelines.
While pregnant with a single baby, women at a healthy weight before pregnancy gain should gain 25 to 35 pounds; overweight women should aim for 15 to 25 pounds; and obese women should restrict their pregnancy weight gain to 11 to 20 pounds, according to guidelines by the Institute of Medicine.
Fully 70% of those women who were obese before they became pregnant exceeded the weight gain guidelines, compared with 31% of those who were at a healthy weight before pregnancy. Still, women who put on more than the recommended weight gave birth to significantly fatter babies regardless of their pre-pregnancy weight, the study showed.
Newborns underwent measurements of length, weight, and fat within 48 hours of birth via a new infant body composition system that requires the infant to lie in a machine for two minutes. Babies born to moms who gained too much weight during pregnancy had 17.5 ounces of body fat, compared with 13.9 ounces of fat among those newborns born to mothers of women who stayed within the guidelines,
This higher obesity risk existed even when birth weight was normal, the study showed.
The message is clear, says Josefson. "Be at as healthy of a weight as you can before becoming pregnant and gain weight within the guidelines," she says. "If you gain too much weight during pregnancy, it can have a negative effect on your child's risk of obesity. And it is also harder to lose this weight, so when you start your next pregnancy, your baby is at a higher risk to begin with."
Eating a healthy diet and sticking to the recommended guidelines for weight gain is important for the long-term health of your baby, she says.
"This is a well-done study," says Hugh S. Taylor, MD, a professor and director of the division of reproductive endocrinology and infertility at Yale University School of Medicine in New Haven, Conn, in an email. "Excessive weight gain leads to fat babies [and] the effect occurred in both obese and normal- weight mothers. However the obese women gained more weight."
Exactly why this occurs is not fully understood. "The women do not need to have a disease such as gestational diabetes [but] due to the higher insulin and glucose levels, I would speculate that increased insulin resistance in the culprit," he says. Moms in the study who gained more than the recommended amounts of weight did have higher levels of blood sugar (glucose), but did not have diabetes.
Some of the women in the study may have had undiagnosed mild insulin resistance in pregnancy, Taylor says.
"Pregnant women should know that they must stick to weight gain guidelines provided by their obstetrician," he says. "Do not gain excessive amounts of weight while pregnant or you will make your baby fat."