Prepregnancy body mass index and risk of preterm birth: association heterogeneity by preterm subgroups.
Parker MG, Ouyang F, Pearson C, Gillman MW, Belfort MB, Hong X, Wang G, Heffner L, Zuckerman B, Wang X. Prepregnancy body mass index and risk of preterm birth: association heterogeneity by preterm subgroups. BMC Pregnancy Childbirth. 2014 Apr 30; 14:153.