Department of Obstetrics and Gynecology, College of Medicine, University of Lagos, Lagos, Nigeria. Department of Obstetrics and Gynecology, Lagos University Teaching Hospital, Lagos, Nigeria. Department of Hematology and Blood Transfusion, College of Medicine, University of Lagos, Lagos, Nigeria. AIDS Prevention Initiative in Nigeria (APIN) Clinic, Lagos University Teaching Hospital, Lagos, Nigeria. Department of Community Health and Primary Health Care, College of Medicine, University of Lagos, Lagos, Nigeria. Department of Obstetrics and Gynecology, Lagos State University Teaching Hospital, Ikeja, Nigeria. Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA, USA.