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Gaining too much weight during pregnancy nearly doubles risk of having a heavy baby

October 31, 2008

A study by the Kaiser Permanente Center for Health Research of more than 40,000 women and their babies found that women who gained more than 40 pounds during their pregnancies were nearly twice as likely to have a heavy baby. Published in the November issue of Obstetrics & Gynecology, the study found that more than one in five women gains excessive weight during pregnancy, doubling her chances of having a baby that weighs 9 pounds or more.

"Too many women gain too much weight during pregnancy. This extra weight puts them at higher risk for having heavy babies, and these babies are programmed to become overweight or obese later in life," said study lead author Teresa Hillier, MD, MS, an endocrinologist and senior investigator at the Kaiser Permanente Center for Health Research in Oregon and Hawaii. "A big baby also poses serious risks for both mom and baby at birth--for mothers, vaginal tearing, bleeding, and often C-sections, and for the babies, stuck shoulders and broken collar bones. "

While researchers have known for some time about the link between diabetes during pregnancy and heavier birth weights, and recently have learned how maternal weight gain affects the birth weight, this is the first study to determine that women who gain excessive weight are even more likely to have heavy babies than women who are treated for gestational diabetes.

"This is one more good reason to counsel women to gain the ideal amount of weight when they are pregnant," said study co-author Kim Vesco, MD, MPH, an obstetrician and gynecologist with Kaiser Permanente in Portand, Oregon. "From a practical standpoint, women who gain too much weight during pregnancy can have a very difficult time losing the weight after the baby is born."

The study followed 41,540 women who gave birth in Washington, Oregon and Hawaii from 1995-2003. More than 20 percent of the women who gained more than 40 pounds-which is the maximum recommended pregnancy weight gain--- gave birth to heavy babies. In contrast, less than 12 percent of women with normal weight gain had heavy babies.

At greatest risk were the women who gained more than 40 pounds and also had gestational diabetes; nearly 30 percent of them had heavy babies. That risk was significantly reduced-- to only 13 percent-- when women with gestational diabetes gained less than 40 pounds.

"The take-home message is that all pregnant women need to watch their weight gain, and it is especially important for women who have risk factors like gestational diabetes." Dr. Hillier said.

Kaiser Permanente Center for Health Research