1. From the Departments of Obstetrics & Gynecology and Medicine, Division of Biological Sciences (M.D.L.), University of Chicago, Ill; Perinatology Research Branch (R.R.), Division of Intramural Research, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, Md; and the Center for Molecular Medicine and Genetics (R.R.), Wayne State University School of Medicine, Detroit, Mich.