LAS VEGAS – Two similar behavioral interventions during pregnancy both succeeded in capping gestational weight gain in two independent randomized trials, but neither intervention produced improvements in obstetrical outcomes.

Results from several prior studies linked excess gestational weight gain (GWG) with adverse outcomes, including gestational diabetes, hypertension, macrosomia, and cesarean delivery. But none of the rates of these complications fell among women in the study groups that received intervention and had reduced GWG, compared with controls.

“The clinical significance of the difference in GWG we saw is not known,” said Alison G. Cahill, MD, who presented one of the two reports at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine. In the study she led, women who received a behavioral intervention averaged about 3.5 pounds less GWG through 36 weeks of pregnancy.

“Our findings call into question the association between GWG and adverse pregnancy outcomes,” said Alan M. Peaceman, MD, who presented the second study, in which women receiving the behavioral intervention averaged 4 pounds less in GWG, compared with control women.

Dr. Peaceman reported results from the Maternal Offspring Metabolics: Family Intervention Trial (MOMFIT), a trial run at Northwestern University in Chicago that randomized 263 pregnant women. The women had to be at less than 16 weeks singleton gestation with a body mass index of 25-40 kg/m², no pregestational diabetes, and a first trimester weight gain of no more than 15 pounds.

The researchers randomized participants to receive either an intervention that included an individualized diet, Internet-based self monitoring of diet adherence, recommendations on physical activity, and weekly coaching calls and opportunities for group meetings, webinars and podcasts; or a control regimen of electronic newsletters and website access that dispensed pregnancy information without mentioning diet. The participants averaged 33 years old, their average body mass index was 31 kg/m², and about 55% were obese, with a body mass index of 30 kg/m₂ or greater.

The study’s primary outcome was weight gain from enrollment through 36 weeks of gestation, which averaged 19.1 pounds among women who received the intervention and 23.7 pounds among controls, an average 4.6 pounds difference that was statistically significant, Dr. Peaceman reported.

The percentage of patients exceeding the GWG recommendations made in 2009 by the Institute of Medicine (IOM) was 68% in the intervention group and 86% among the controls, an 18 percentage-point difference that was statistically significant.

Despite these differences, the two groups showed very similar rates for the incidence of gestational diabetes, preeclampsia or hypertension, birth weight above 4,000 g, and gestational age at delivery (39 weeks on average for both subgroups).

The rate of cesarean delivery (40%) was higher in the women who received the intervention and had less GWG, compared with 27% among the control women. Despite meeting the statistical test for significance, it is most likely a chance result, said Dr. Peaceman, chief of maternal fetal medicine at Northwestern.

He stressed that while no benefit from reduced GWG has yet been found in the MOMFIT results, additional endpoints are under study, such as neonatal metabolism, infant metabolism at 1 year, and maternal weight retention.

Dr. Cahill reported very similar findings from her study, run as part of the Weight Management in Obese Pregnant Underserved African American Women (LIFE-Moms) trial. She enrolled 267 socioeconomically disadvantaged African American women with singleton, normal-anatomy pregnancies who presented for prenatal care at her clinic at less than 16 weeks gestation and were overweight or obese.

The study randomized these women to receive either an exercise and lifestyle intervention along with home visits from the Parents as Teachers program, or just home visits without the exercise and lifestyle component. The enrolled women averaged about 25 years old, and their average body mass index was about 32 kg/m², with two-thirds of patients being obese.

The study’s primary endpoint, the percentage of women who exceeded the IOM’s 2009 recommendations on GWG, was 37% among women who received the exercise and lifestyle intervention and 46% among those who did not, a difference that was not statistically significant in the full intention-to-treat analysis, Dr. Cahill reported.

A subgroup analysis showed that most of the benefit focused in obese participants, where 34% of women who received the extra intervention had a GWG greater than the IOM recommendation, compared with a 49% rate among controls, a 15 percentage-point difference that fell just short of statistical significance.

For the secondary endpoint of average amount of GWG, women in the intervention arm had a 8.05 kg average, compared with 9.64 kg among the controls, an average GWG reduction of 1.59 kg (3.5 pounds) in the intervention arm. This difference was statistically significant, said Dr. Cahill, chief of maternal fetal medicine at Washington University in St. Louis.

Dr. Cahill also ran a modified intention-to-treat analysis that excluded women with missing GWG data at term, those with fetal death or miscarriage, and one women mistakenly enrolled who was of normal weight. Among the remaining 240 women, the impact of the exercise and lifestyle intervention was even more pronounced, resulting in an average reduction in GWG of 4 pounds and a 12 percentage-point reduction in women exceeding the IOM’s GWG recommendations.

Despite these favorable effects on GWG, the two study arms showed no significant differences in the incidence of gestational diabetes, gestational hypertension, preterm births, or cesarean delivery.

Dr. Cahill said that she too planned to look at additional outcomes that might be affected by controlling GWG, including maternal weight retention and neurodevelopment in the children.

mzoler@frontlinemedcom.com On Twitter @mitchelzoler

Capping gestational weight gain didn’t deliver better pregnancy outcomes