Weight Gain During Pregnancy Links To Bigger Babies

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According to a new study, expected mothers gaining 40 pounds or more during pregnancy results in 9 pound or more babies and increasing health risks for both the mother and child.

Excessive pregnancy weight gain and big babies have often been linked, says Teresa Hillier, MD, senior investigator at the Kaiser Permanente Center for Health Research, Portland, Ore., and the study’s lead author. Researchers have also known that women who develop diabetes during pregnancy, called gestational diabetes, are more likely to deliver heavier babies, Hillier states.

But the new study is believed the first to conclude that women who gain excessive weight during pregnancy are even more likely to have heavier babies than women treated for gestational diabetes who don’t gain excess weight.

“More than one in five women gain too much weight during pregnancy and only 5% have gestational diabetes,” Hillier tells states. The study, she says, points to the need for all women to follow recommendations about not gaining excessive amounts of weight.

Pregnancy Weight Gain & Big Babies: Study Details

Hillier and her colleagues followed 41,540 women who gave birth to singleton babies in Washington, Oregon, and Hawaii from 1995 through 2003. They used patient medical records and birth certificates to note the mother’s weight gain and the baby’s birth weight.

All mothers-to-be were screened for gestational diabetes.

The researchers analyzed the numbers of women who gained more than 40 pounds — the maximum recommended weight gain — and whether their babies weighed more than about 9 pounds at birth, which is considered a heavy baby.

Heavier babies are at risk of becoming heavy adults, Hillier says, and make it more likely the mother will have to deliver by cesarean section, among other increased health risks.

Pregnancy Weight Gain & Big Babies: Study Results

Overall, 12.5% of the babies — or 5,182 — were born weighing 8.8 pounds or more.

Overall, more than 20% of those who gained more than 40 pounds gave birth to heavy babies, and less than 12% of those who gained less than 40 pounds had heavy babies.

Other results suggest that excess weight gain — whether or not a woman has gestational diabetes — boosts the risk of having a heavy baby.

  • While 16.5% of women with normal glucose who gained more than 40 pounds had a heavy baby, only 9.3% of those who had normal glucose levels who gained less than 40 pounds had a heavy baby.
  • While 29.3% of women with gestational diabetes who gained more than 40 pounds had big babies, just 13.5% of those with gestational diabetes who gained 40 pounds or less did.

“Gestational diabetes puts the baby in an overfed state,” Hillier says. “When a mother gains too much weight, even if she has normal glucose levels, the baby is overfed in a similar way.”

Big babies are also more likely to get stuck during vaginal deliveries, she says, and to be injured.