[1] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Div Intramural Populat Hlth Res, Epidemiol Branch, Rockville, MD USA
[2] Penn State Univ, Dept Obstet & Gynecol, Hershey, PA 17033 USA
[3] Augusta Univ, Dept Obstet & Gynecol, Augusta, GA USA
[4] Univ Penn, Sch Med, Dept Obstet & Gynecol, Philadelphia, PA 19104 USA
[5] Univ N Carolina, Dept Obstet & Gynecol, Chapel Hill, NC USA
[6] Univ Colorado Anschutz Med Campus, Dept Obstet & Gynecol, Aurora, CO USA
[7] Univ Michigan, Dept Obstet & Gynecol, Ann Arbor, MI 48109 USA
[8] Univ Vermont, Dept Obstet & Gynecol, Burlington, VT USA
[9] Yale Univ, Sch Publ Hlth, Dept Biostat, New Haven, CT USA
[10] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Fertil & Infertil Branch, Rockville, MD USA
[11] Univ Calif San Francisco, Dept Obstet Gynecol & Reprod Sci, 1635 Div St,Suite 601, San Francisco, CA 94115 USA