Leonard SA, et al. - Using linked birth certificate and hospitalisation discharge records from Californian births during 2007-2012, researchers assessed the connection between body mass index (BMI) and severe maternal morbidity (SMM) pregnancy in a large, diverse birth cohort and evaluated potential mediation through obesity-related co-morbidities (hypertensive conditions, diabetes, asthma) and caesarean birth. Data reported that the SMM prevalence was 1.42% among 2,650,182 births. The association between high pregnancy BMI and SMM was explained by co-morbidities and caesarean birth. These findings suggest that promoting healthy pregnancy weight, along with co-morbidity management and supporting vaginal birth in pregnant women with high BMI, may reduce the risk of SMM. However, the high risk of SMM observed in women with low BMI was not reduced by these mediators.