1. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, School of Medicine, Chapel Hill, North Carolina.
2. Department of Maternal-Child Health, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, North Carolina.
3. Departments of Family and Social Medicine and Obstetrics, Gynecology & Women's Health, Albert Einstein College of Medicine, New York, New York.