1. Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts.
2. Department of Obstetrics, Gynecology, and Reproductive Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
3. Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts.
4. Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.