Weight gain during pregnancy may increase risk of severe maternal morbidity

Gestational weight gain (GWG), both high and low, appears to increase the risk of severe maternal morbidity (SMM) across body mass index (BMI) groups, suggests a recent study. However, low weight gain and weight loss in women with class 3 obesity may lower the risk of SMM.

The authors analysed administrative records from 2,483,684 births in California (2007–2012), with z score charts used to standardize GWG for gestational duration. Z scores were fit nonlinearly, while GWG was categorized as above, within or below the Institute of Medicine (IOM) recommendations after predicting equivalent GWG at term from the z score charts.

A validated index was utilized to define SMM. Multivariable logistic regression models were used to estimate associations.

A generally shallow U-shaped association was observed between GWG z score and SMM in all BMI groups, except class 3 obesity (≥40 kg/m²), for which weight loss correlated with the lowest risk. The weight gain amount associated with the lowest SMM risk was within the IOM recommendations for underweight and class 2 obesity but above for normal weight, overweight and class 1 obesity.

Adjusted risk ratios (RRs) for GWG below vs within the IOM recommendations were 1.13 (95 percent confidence interval [CI], 0.99–1.29) for underweight, 1.09 (95 percent CI, 1.04–1.14) for normal weight, 1.10 (95 percent CI, 1.01–1.19) for overweight, 1.07 (95 percent CI, 0.95–1.21) for class 1 obesity, 1.03 (95 percent CI, 0.88–1.22) for class 2 obesity, and 0.89 (95 percent CI, 0.73–1.08) for class 3 obesity.

The corresponding RRs for GWG above the IOM recommendations were 0.99 (95 percent CI, 0.84–1.15), 1.04 (95 percent CI, 0.99–1.08), 0.98 (95 percent CI, 0.92–1.04), 1.03 (95 percent CI, 0.95–1.13), 1.07 (95 percent CI, 0.94–1.23), and 1.08 (95 percent CI, 0.91–1.30).