[1] Univ N Carolina, Sch Med, Div Maternal Fetal Med, Dept Obstet & Gynecol, Chapel Hill, NC 27599 USA
[2] Ohio State Univ, Ohio State Coll Med, Columbus, OH 43210 USA
[3] Brown Univ, Sch Med, Providence, RI 02912 USA
[4] Univ Texas Hlth Sci Ctr Houston, Houston, TX USA
[5] Univ Texas SW Med Ctr Dallas, Dallas, TX 75390 USA
[6] Columbia Univ, Coll Phys & Surg, New York, NY USA
[7] Univ Utah, Sch Med, Salt Lake City, UT USA
[8] Univ Alabama Birmingham, Sch Med, Birmingham, AL USA
[9] Drexel Univ, Coll Med, Philadelphia, PA 19104 USA
[10] Case Western Reserve Univ, Metrohlth Med Ctr, Sch Med, Cleveland, OH USA
[11] Wake Forest Univ Hlth Sci, Winston Salem, NC USA
[12] Univ Texas Med Branch, Galveston, TX USA
[13] Wayne State Univ, Sch Med, Detroit, MI USA
[14] Northwestern Univ, Feinberg Sch Med, Chicago, IL 60611 USA
[15] Oregon Hlth & Sci Univ, Portland, OR 97201 USA
[16] George Washington Univ, Ctr Biostat, Washington, DC USA
[17] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Bethesda, MD USA