[1] Mel & Enid Zuckerman Coll Publ Hlth, Dept Epidemiol & Biostat, Tucson, AZ 85724 USA
[2] Coll Med Tucson, Dept Obstet & Gynecol, Tucson, AZ 85724 USA
[3] Univ Arizona, Tucson, AZ USA
[4] Dartmouth Hitchcock, Dept Obstet & Gynecol, Nashua, NH USA
[5] Bur Family Hlth & Nutr, Massachusetts Dept Publ Hlth, Boston, MA 02108 USA
[6] Boston Univ, Dept Biostat, Sch Publ Hlth, Boston, MA USA
[7] Carolinas Med Ctr Atrium Hlth, Dept Obstet & Gynecol, Charlotte, NC USA
[8] Oregon Hlth & Sci Univ, Dept Pediat, Portland, OR USA
[9] Univ Colorado, Dept Pediat, Sect Neonatol, Sch Med, Aurora, CO USA
[10] Michigan State Univ, Coll Human Med, Dept Obstet Gynecol & Reprod Biol, Grand Rapids, MI USA
[11] Harvard TH Chan Sch Publ Hlth, Dept Epidemiol, Boston, MA USA