[1] Massachusetts Gen Hosp, Vincent Dept Obstet & Gynecol, Boston, MA 02114 USA
[2] Harvard Med Sch, Dept Obstet Gynecol & Reprod Biol, Boston, MA USA
[3] Michigan State Univ, Coll Human Med, Dept Obstet Gynecol & Reprod Biol, E Lansing, MI 48824 USA
[4] Univ Rochester, Dept Obstet & Gynecol, Sch Med, Rochester, NY USA
[5] Johns Hopkins Univ, Sch Med, Dept Obstet & Gynecol, Baltimore, MD 21205 USA
[6] Stanford Univ, Sch Med, Dept Obstet & Gynecol, Palo Alto, CA 94304 USA
[7] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, NIH, Bethesda, MD USA
[8] Univ Colorado, Sch Med, Dept Obstet & Gynecol, Aurora, CO USA