[1] Cook Cty Hosp, Dept Obstet & Gynecol, Chicago, IL 60612 USA
[2] Johns Hopkins Sch Publ Hlth, Dept Epidemiol, Baltimore, MD USA
[3] NICHHD, Bethesda, MD 20892 USA
[4] Univ So Calif, Div Hematol, Los Angeles, CA USA
[5] Univ Calif San Francisco, Dept Med, San Francisco, CA 94143 USA
[6] Lincoln Med & Mental Hlth Ctr, Bronx, NY 10451 USA
[7] Maimonides Hosp, Dept Obstet & Gynecol, Brooklyn, NY 11219 USA