Nuance Needed Regarding Weight-Gain Recommendations During Pregnancy

December 21, 2023 • by Esther Robards-Forbes

Patients with obesity while pregnant may receive recommendations from their doctors that need revisiting, researchers say.

A pregnant person, left, speaks with a doctor, right, while she points at a clipboard.

When a patient expecting a baby has a body mass index above 30, doctors typically recommend gaining 5-9 kg (about 11-20 pounds) during the course of pregnancy. But researchers at The University of Texas at Austin and Kaiser Permanente Northern California say new evidence points to the need for greater nuance when it comes to these recommendations. Their new study has found patients who gained less than the recommended amount or kept their weight stable could have better outcomes than those that met the recommendations. 

The gestational weight gain guidelines were introduced by the National Academy of Medicine in 2009, but the new study makes distinctions about variations in obesity in patients that the guidelines do not. While the guidelines group everyone with a BMI over 30 into one category, in the study out this month in the American Journal of Perinatology, researchers grouped patients by obesity class at the start of pregnancy, which is specific to their BMI. More than 29,000 patients in Obesity Class I (BMI 30-34.9), Class II (BMI 35-39.9) and Class III (BMI 40+), and researchers examined birth outcomes such as infant birth weight, cesarean section, admission to the neonatal intensive care unit and preterm births.

“The common thinking is that gaining less than the recommended amount of weight during pregnancy increases risk of negative outcomes, but we found some positive effects for some patients with obesity when they gained less or no weight at all,” said Elizabeth Widen, UT assistant professor of nutritional sciences and lead author of this study. 

Researchers compared patients with obesity who gained the recommended amount of weight to patients who lost weight, gained less than the recommended amount or maintained a stable weight throughout their pregnancy. In the United States, almost 1 in 3 of those who are newly pregnant — 29 percent — have a BMI classified in the obesity with the majority of those in Class I. 

“We need different recommendations on weight gain during pregnancy that are tailored to people’s obesity class,” said Monique Hedderson, co-author of this study and Associate Director, Women's and Children's Health at Kaiser Permanente Northern California.

Weight loss during pregnancy proved almost uniformly risky: it was associated with babies being born too small for their gestational age at birth. Other outcomes, however, were more mixed. For those with Class I and Class II obesity, weight stability across pregnancy was associated with increased risk of a baby being born too small, but interestingly among those with Class II was protective for C-section. For those with Class III obesity, though, low weight gain and weight stability were not associated with any negative outcomes, and the risk of C-sections and babies born large for gestational age was markedly reduced. 

“This shows us that energy stores in the body can potentially be mobilized to support a pregnancy in people with higher BMI values at the onset of pregnancy, and that low weight gain and weight stability may be safe as long as the baby is growing appropriately,” Widen said. 

Amy R. Nichols, Lorie Harper, Alison Cahill, Jaimie N. Davis, Saralyn F. Foster and Rachel R. Rickman of UT Austin and Fei Xu and Monique M. Hedderson of Kaiser Permanente Northern California were also authors on the paper. The research was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Kaiser Permanente Northern California and the National Institute of Diabetes and Digestive and Kidney Diseases.

Widen and Saralyn Foster, two of the authors on this paper, were recently featured in the latest segment of an ongoing video series called Nexus Points, highlighting researchers in the College of Natural Sciences.