Leonard SA, et al. - Researchers here examined if and how gestational weight gain (GWG) is associated with severe maternal morbidity (SMM) by prepregnancy BMI group. Administrative records from 2,483,684 Californian births (2007–2012) were analyzed using z score charts to standardize GWG for gestational duration. In all BMI groups, except class 3 obesity (≥ 40 kg/m²), high and low GWG may be modestly associated with increased risk of SMM. For class 3 obesity (≥ 40 kg/m²) group, risk was lowest with weight loss. For underweight and class 2 obesity, the weight gain amount linked with the lowest risk of SMM was within the Institute of Medicine (IOM) recommendations, but for normal weight, overweight, and class 1 obesity, it was above the IOM recommendations.