[1] Emory Univ, Sch Med, Dept Pediat, Atlanta, GA 30322 USA
[2] Childrens Healthcare Atlanta, Atlanta, GA USA
[3] Natl Ctr Chron Dis Prevent & Hlth Promot, Div Reprod Hlth, Atlanta, GA USA
[4] Ctr Dis Control & Prevent, Div Unintent Injury Prevent, Natl Ctr Injury Prevent & Control, Atlanta, GA USA