Stopping breastfeeding before 6 months ( HR 2.4 ; 95 % CI 1.2-5 .1 ) and low birthweight ( HR 2.4 ; 95 % CI 1.3-4 .3 ) were found to increase the risk of a severe event , whilst maternal completion of high school education was protective ( HR 0.3 ; 95 % CI 0.1-0 .7 ) .