[1] Emory Univ, Sch Med, Dept Family & Prevent Med, Atlanta, GA 30322 USA
[2] Boston Univ, Med Ctr, Dept Family Med, Boston, MA USA
[3] Univ Med & Dent New Jersey, Sch Osteopath Med, Dept Obstet & Gynecol, Div Maternal Fetal Med, Stratford, NJ 08084 USA
[4] Univ Calif Los Angeles, Dept Obstet & Gynecol, Sch Publ Med, Los Angeles, CA 90024 USA
[5] Univ Calif Los Angeles, Dept Obstet & Gynecol, Sch Publ Hlth, Los Angeles, CA 90024 USA
[6] Univ Calif Los Angeles, Dept Community Hlth Sci, Sch Publ Med, Los Angeles, CA USA
[7] Univ Calif Los Angeles, Sch Publ Hlth, Dept Community Hlth Sci, Los Angeles, CA 90024 USA
[8] Duke Univ, Med Ctr, Dept Obstet & Gynecol, Durham, NC 27710 USA
[9] Ohio State Univ, Coll Med, Dept Obstet & Gynecol, Div Maternal Fetal Med, Columbus, OH 43210 USA
[10] Bur Child & Family Hlth Serv, Columbus, OH USA
[11] Tulane Univ, Dept Obstet & Gynecol, New Orleans, LA 70118 USA
[12] NIH, Natl Human Genome Project Res Inst, Bethesda, MD USA
[13] Univ N Carolina, Dept Obstet & Gynecol, Chapel Hill, NC USA