[1] Northwestern Univ, Dept Obstet & Gynecol, 250 East Super St,Suite 05-2175, Chicago, IL 60611 USA
[2] RTI Int, Div Biostat & Epidemiol, Res Triangle Pk, NC USA
[3] Univ Calif Irvine, Dept Obstet & Gynecol, Irvine, CA 92717 USA
[4] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Bethesda, MD USA
[5] Univ Pittsburgh, Dept Obstet & Gynecol, Pittsburgh, PA USA
[6] Univ Utah, Hlth Sci Ctr, Dept Obstet & Gynecol, Salt Lake City, UT USA
[7] Columbia Univ, Dept Obstet & Gynecol, New York, NY USA
[8] Univ Penn, Dept Obstet & Gynecol, Philadelphia, PA 19104 USA
[9] Case Western Reserve Univ, Metrohlth Med Ctr, Dept Obstet & Gynecol, Cleveland, OH USA
[10] Indiana Univ, Dept Obstet & Gynecol, Indianapolis, IN 46204 USA
[11] Christiana Care Hlth Syst, Dept Obstet & Gynecol, Newark, DE USA
[12] Ohio State Univ, Dept Obstet & Gynecol, Columbus, OH 43210 USA
[13] Univ Texas Med Branch, Dept Obstet & Gynecol, Galveston, TX 77555 USA