1 Department of Obstetrics and Gynecology, Riverside Health System, Newport News, Virginia Georgetown University School of Medicine, Washington, DC Department of Obstetrics and Gynecology, Riverside Health System, Newport News, Virginia Department of Biostatistics and Bioinformatics, MedStar Health Research Institute, Washington, DC Department of Prevention and Community Health, George Washington University School of Public Health and Health Services, Washington, DC Department of Obstetrics and Gynecology, MedStar Washington Hospital Center and Children's National Medical Center, Washington, DC.