Charts of all women aged 19 and younger (n = 1,354) having singleton live births in 2004, 2005, and 2006 were retrieved. For the adult group, 1,389 charts of mothers between the ages of 20 and 34 delivering singleton babies were selected using proportionate systematic random sampling. Maternal age was divided into 3 groups: 11–15, 16–19, and 20–34.