Study Challenges Notions on Pregnancy Weight Gain in Women with Obesity

The study supports calls to lower or remove the lower limit of current US Institute of Medicine (IOM) recommendations for pregnant women with obesity and suggests warranting separate guidelines for class 3 obesity.

"Gaining less weight than is recommended was associated with better outcomes among those with prepregnancy BMIs >40 kg/m2," the researchers reported.

There are concerns that current gestational weight gain recommendations for obese women are too high and that guidelines should differ based on the severity of obesity. In the study, Kari Johansson, Karolinska Institutet, Stockholm, Sweden, and colleagues investigated the safety of gestational weight gain below current recommendations or weight loss in pregnancies with obesity. They evaluated whether there is a need for separate guidelines for different obesity classes.

In the population-based cohort study, the researchers used electronic medical records from the Stockholm–Gotland Perinatal Cohort study to identify pregnancies with obesity (early pregnancy BMI before 14 weeks' gestation ≥30 kg/m2) among singleton pregnancies with deliveries between 2008 and 2015. The pregnancy records were linked with Swedish national healthcare register data up to 2019. Gestational weight gain was calculated as the last measured weight before or at delivery minus early pregnancy weight (at <14 weeks gestation), standardized for gestational age into z-scores.

Poisson regression assessed the association of gestational weight gain z-score with a composite outcome of infant death, stillbirth, small for gestational age and large for gestational age at birth, unplanned cesarean delivery, preterm birth, pre-eclampsia, gestational diabetes, and excess postpartum weight retention, and new-onset longer-term maternal cardiometabolic disease following pregnancy, weighted to account for event severity.

Rate ratios (RRs) were calculated for composite adverse outcomes along the weight gain z-score continuum, compared with a reference of the current lower limit for gestational weight gain recommended by the US IOM (5 kg at term).

The study revealed the following findings:

· The cohort comprised 15 760 pregnancies with obesity, followed up for a median of 7·9 years.

· 74·0% of pregnancies had class 1 obesity, 20·1% had class 2 obesity, and 5·9% had class 3 obesity. Among these pregnancies, 13·9%, 24·9%, and 33·2%, respectively, had weight gain during pregnancy below the lower limit of the IOM recommendation (5 kg).

· In pregnancies with class 1 or 2 obesity, gestational weight gain values below the lower limit of the IOM recommendation or weight loss did not increase the risk of the adverse composite outcome (e.g., at weight gain z-score –2·4, corresponding to 0 kg at 40 weeks: adjusted RR 0·97 in obesity class 1 and 0·96 in obesity class 2).

· In pregnancies with class 3 obesity, weight gain values below the IOM limit or weight loss were associated with reduced risk of the adverse composite outcome (e.g., adjusted RR 0·81 at weight gain z-score –2·4, or 0 kg).

These results challenge guidelines on weight gain in pregnancy. Particularly for women with class 3 obesity, the findings support minimizing pregnancy weight gain — as long as nutritional balance is maintained.

"Careful counseling on healthy pregnancy nutrition at prenatal visits, considering referral for enhanced supports for those with obesity, and addressing barriers to access healthful food might help optimize outcomes for pregnancies affected by obesity," the researchers concluded.

Reference:

Johansson K, Bodnar LM, Stephansson O, Abrams B, Hutcheon JA. Safety of low weight gain or weight loss in pregnancies with class 1, 2, and 3 obesity: a population-based cohort study. Lancet. 2024 Apr 13;403(10435):1472-1481. doi: 10.1016/S0140-6736(24)00255-1. Epub 2024 Mar 28. PMID: 38555927; PMCID: PMC11097195.