The researchers had found evidence of this link in two previous studies, said coauthor Laura Schieve, an epidemiologist with CDC’s National Center on Birth Defects and Developmental Disabilities. Schieve and her co-authors studied data on 1,311 mother-child pairs collected between 2005 and 2012, including the mothers’ body mass index (BMI, a height-to-weight ratio) before pregnancy and their reports of the children’s psychosocial difficulties at age six.