[1] Univ Alabama Birmingham, Dept Pediat, Birmingham, AL 35249 USA
[2] Univ Rochester, Med Ctr, Dept Pediat, Rochester, NY 14642 USA
[3] Stat & Epidemiol Unit RTI Int, Res Triangle Pk, NC USA
[4] Ctr Dis Control & Prevent, Natl Ctr Birth Defects & Dev Disabil, Atlanta, GA USA
[5] Univ Aarhus, NANEA Dept Epidemiol, Inst Publ Hlth, Aarhus, Denmark
[6] Ctr Dev Biol & Perinatal Med, Pregnancy & Perinatol Branch, Neonatal Res Network, Bethesda, MD USA