[1] UC San Diego Hlth Syst, Dept Obstet Gynecol & Reprod Sci, San Diego, CA USA
[2] RTI Int, Social Stat & Environm Sci, Res Triangle Pk, NC USA
[3] Univ Pittsburgh, Sch Med, Dept Urol, Pittsburgh, PA USA
[4] Univ Texas Southwestern Med Ctr Dallas, Dept Obstet & Gynecol, Dallas, TX 75390 USA
[5] Univ Penn, Dept Obstet & Gynecol, Philadelphia, PA 19104 USA
[6] Univ Alabama Birmingham, Dept Obstet & Gynecol, Birmingham, AL 35294 USA
[7] Brown Univ, Dept Obstet & Gynecol, Providence, RI 02912 USA
[8] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, NIH, Bethesda, MD USA