Pregnant women can safely limit their weight gain with diet and exercise interventions, the results of a group of trials by the US National Institutes of Health (NIH) show.
Many overweight and obese women gain too much weight during pregnancy, further ratcheting up the already increased risk of serious complications for themselves and their babies such as childhood obesity or diabetes.
However, the reduced weight gain -- about four pounds per woman -- did not result in fewer obstetrical complications, including caesarean sections, diabetes, hypertension, and preeclampsia, or change the average birth weight of the baby.
It could be because "by the time these women are already in the second trimester, it may already be late to change important outcomes", Peaceman said.
"To lower the risk of obstetrical complications, they may have to start changing their lifestyle before or immediately after they conceive," he noted.
For the study, published in the journal Obesity, the teams recruited 1,150 participants (579 women had the lifestyle intervention, 571 had standard care), which ran from the second trimester to birth.
Each trial offered a varied lifestyle intervention but all aimed to improve diet quality and reduce calories, increase physical activity and incorporate behaviour strategies such as self-monitoring.
Overweight and obese women are a critical group to target because they have higher rates of excess pregnancy weight gain and of retaining that weight postpartum. They are also more likely to have children who are obese.