[1] Ohio State Univ, Coll Med & Publ Hlth, Dept Obstet & Gynecol, Columbus, OH 43210 USA
[2] George Washington Univ, Ctr Biostat, Dept Obstet & Gynecol, Washington, DC USA
[3] NICHHD, Dept Obstet & Gynecol, Bethesda, MD 20892 USA
[4] Univ Alabama, Dept Obstet & Gynecol, Birmingham, AL 35294 USA
[5] Univ Texas, SW Med Ctr, Dept Obstet & Gynecol, Dallas, TX 75235 USA
[6] Univ Utah, Dept Obstet & Gynecol, Salt Lake City, UT USA
[7] Univ Chicago, Dept Obstet & Gynecol, Chicago, IL 60637 USA
[8] Univ Pittsburgh, Dept Obstet & Gynecol, Pittsburgh, PA USA
[9] Wake Forest Univ, Dept Obstet & Gynecol, Winston Salem, NC 27109 USA
[10] Thomas Jefferson Univ, Dept Obstet & Gynecol, Philadelphia, PA 19107 USA
[11] Wayne State Univ, Dept Obstet & Gynecol, Detroit, MI USA
[12] Univ Cincinnati, Dept Obstet & Gynecol, Cincinnati, OH USA
[13] Columbia Univ, Dept Obstet & Gynecol, New York, NY USA
[14] Brown Univ, Dept Obstet & Gynecol, Providence, RI 02912 USA
[15] Northwestern Univ, Dept Obstet & Gynecol, Chicago, IL 60611 USA
[16] Univ Miami, Dept Obstet & Gynecol, Miami, FL 33152 USA
[17] Univ Tennessee, Dept Obstet & Gynecol, Memphis, TN 38103 USA
[18] Univ Texas, Hlth Sci Ctr, Dept Obstet & Gynecol, San Antonio, TX 78284 USA
[19] Univ N Carolina, Dept Obstet & Gynecol, Chapel Hill, NC USA
[20] Univ Texas, Hlth Sci Ctr, Dept Obstet & Gynecol, Houston, TX USA
[21] Case Western Reserve Univ, Dept Obstet & Gynecol, Cleveland, OH 44106 USA
[22] Vanderbilt Univ, Dept Obstet & Gynecol, Nashville, TN USA