Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD; the Departments of Obstetrics and Gynecology, the University of Texas Medical Branch at Galveston, Galveston, Texas, the University of Utah Health Sciences Center, Salt Lake City, Utah, the University of Texas McGovern Medical School at UT Health, Houston, Texas, the University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, the University of Alabama at Birmingham, Birmingham, Alabama, Columbia University, New York, New York, Northwestern University, Chicago, Illinois, The Ohio State University, Columbus, Ohio, MetroHealth Medical Center-Case Western Reserve University, Cleveland, Ohio, Brown University, Providence, Rhode Island, Stanford University, Stanford, California, Wayne State University, Detroit, Michigan, and the University of Pittsburgh, Pittsburgh, Pennsylvania; and the George Washington University Biostatistics Center, Washington, DC.