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.