[1] Univ Alabama Birmingham, Dept Obstet & Gynecol, Div Maternal Fetal Med, 1700 6th Ave South,Room 10270, Birmingham, AL 35233 USA
[2] George Washington Univ, Biostat Ctr, Washington, DC USA
[3] Ohio State Univ, Coll Med, Dept Obstet & Gynecol, Columbus, OH 43210 USA
[4] Univ Utah, Hlth Sci Ctr, Dept Obstet & Gynecol, Salt Lake City, UT USA
[5] Univ Texas Southwestern Med Ctr Dallas, Dept Obstet & Gynecol, Dallas, TX USA
[6] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Bethesda, MD USA
[7] Columbia Univ, Dept Obstet & Gynecol, New York, NY USA
[8] Brown Univ, Dept Obstet & Gynecol, Providence, RI 02912 USA
[9] Univ N Carolina, Dept Obstet & Gynecol, Chapel Hill, NC 27515 USA
[10] Case Western Reserve Univ, Metrohlth Med Ctr, Dept Obstet & Gynecol, Cleveland, OH USA
[11] Univ Texas Med Branch, Dept Obstet & Gynecol, Galveston, TX 77555 USA
[12] Northwestern Univ, Dept Obstet & Gynecol, Chicago, IL 60611 USA
[13] Univ Texas Hlth Sci Ctr Houston, Dept Obstet & Gynecol, Childrens Mem Hermann Hosp, Houston, TX 77030 USA