1Division of Epidemiology, Statistics, and Prevention Research, National Institute of Child Health and Human Development, Department of Health and Human Services, Bethesda, Md., Beth Israel Deaconess Medical Center and Harvard Medical School, Boston
2Departments of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston
3Allied Technology Group, Rockville, MD
4Obstetrics and Gynecology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston
5Departments of Medicine and Obstetrics, Massachusetts General Hospital and Harvard Medical School, Boston
6Harvard School of Public Health, Boston
7Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine, Cincinnati