Moms-to-be who pack on too many prenatal pounds may be doubling their risk for having a high birth weight baby (a baby weighing 8.8 pounds or more at birth), according to a new study from researchers at Children's Hospital in Boston.
Published August 4, 2010, in an online version of the journal The Lancet, the study looked at data from 513,501 women who had two or more live births. Compared with women who gained 18 to 22 pounds (considered a healthy weight gain for normal-weight women), pregnant women who gained 44 to 49 pounds were 1.7 times more likely to have a high birth weight baby; gaining more than 53 pounds made women 2.3 times more likely to have a baby with a high birth weight. As a way of explanation, the study's authors suggest that too much weight gain in pregnancy may create an abnormal uterine environment that changes the baby's brain, pancreas, fat tissue, and other biological systems.
"Hormones and metabolic pathways, and even the structure of tissues and organs that play a role in [a baby's] body weight maintenance are affected," says study co-author Dr. David Ludwig, as quoted in a Los Angeles Times article on the new research.
Because the study only included women who had given birth more than once, researchers were able to compare pregnancy weight gain and birth weights among siblings as a way to rule out any genetic influences on birth weight.
In response to other studies with similar findings, last year the Institute of Medicine released updated guidelines suggesting stricter adherence to weight-gain recommendations for all women and new guidelines to curb weight gain in obese women, the Los Angeles Times points out. What's the right amount of weight gain for you? It's best to find this out from your own doctor or midwife. And it's best to bring this up early on in prenatal care. Your provider can give you feedback on how on many extra calories to eat for gradual weight gain—and how weight gain should be spread out over the course of your pregnancy.