Recent research conducted by The University of Texas at Austin and Kaiser Permanente Northern California suggests a need for nuance in the standard weight-gnain recommendations during pregnancy, particularly for patients with a body mass index (BMI) above 30. While conventional advice suggests gaining 5-9 kg (about 11-20 pounds) for such individuals, the study reveals that outcomes may vary based on obesity class.
The National Academy of Medicine introduced gestational weight gain guidelines in 2009, grouping individuals with a BMI over 30 into a single category. However, the new study, published in the American Journal of Perinatology, distinguishes between obesity classes at the beginning of pregnancy, specific to BMI. Examining more than 29,000 patients in Obesity Class I (BMI 30-34.9), Class II (BMI 35-39.9), and Class III (BMI 40+), researchers delved into birth outcomes such as infant birth weight, cesarean section rates, neonatal intensive care unit admissions, and preterm births.
Lead author Elizabeth Widen, UT assistant professor of nutritional sciences, notes, “The common thinking is that gaining less than the recommended amount of weight during pregnancy increases the risk of negative outcomes, but we found some positive effects for some patients with obesity when they gained less or no weight at all.”
The study compared patients with obesity who followed recommended weight gain to those who lost weight, gained less than recommended, or maintained a stable weight during pregnancy. In the United States, nearly 1 in 3 newly pregnant individuals—29 percent—have a BMI classified as obese, primarily falling into Class I.
Co-author Monique Hedderson, Associate Director, Women’s and Children’s Health at Kaiser Permanente Northern California, suggests the necessity for tailored recommendations based on obesity class, emphasizing, “We need different recommendations on weight gain during pregnancy that are tailored to people’s obesity class.”
Weight loss during pregnancy was uniformly associated with risks, resulting in babies being born too small for their gestational age. However, outcomes varied for weight stability. While it was associated with an increased risk of small babies for those with Class I and Class II obesity, it proved protective against C-sections for Class II individuals. Intriguingly, for those with Class III obesity, low weight gain and weight stability were not linked to negative outcomes, and the risk of C-sections and babies born large for gestational age was significantly reduced.
Lead author Widen interprets the findings, stating, “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.”
The study included additional authors from UT Austin and Kaiser Permanente Northern California, and it 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.
