[1] NICHHD, Bethesda, MD 20892 USA
[2] Eunice Kennedy Shriver NICHD Maternal Fetal Med U, Bethesda, MD USA
[3] George Washington Univ, Ctr Biostat, Washington, DC USA
[4] Univ Utah, Dept Obstet & Gynecol, Salt Lake City, UT USA
[5] Wake Forest Univ Hlth Sci, Dept Obstet & Gynecol, Winston Salem, NC USA
[6] Wayne State Univ, Dept Obstet & Gynecol, Detroit, MI USA
[7] Univ Tennessee, Dept Obstet & Gynecol, Memphis, TN 38103 USA
[8] Brown Univ, Sch Med, Dept Obstet & Gynecol, Providence, RI 02912 USA
[9] Ohio State Univ, Dept Obstet & Gynecol, Columbus, OH 43210 USA
[10] Univ Pittsburgh, Dept Obstet & Gynecol, Pittsburgh, PA USA
[11] Thomas Jefferson Univ, Dept Obstet & Gynecol, Philadelphia, PA 19107 USA
[12] Case Western Reserve Univ, Dept Obstet & Gynecol, Cleveland, OH 44106 USA
[13] Univ Texas Houston, Dept Obstet & Gynecol, Houston, TX USA