Department of Obstetrics and Gynecology, University of Pennsylvania Health System, Philadelphia, Pennsylvania
Center for Clinical Epidemiology and Biostatistics and Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
Leonard Davis Institute for Health Economics, University of Pennsylvania, Philadelphia, Pennsylvania
Women and Infants Hospital, Brown University School of Medicine, Providence, Rhode Island.
Address reprint requests to: George Macones, MD, MSCE, Director, Maternal Fetal Medicine, 2000 Courtyard Building, 3400 Spruce Street, Philadelphia, PA 19104-4283; E-mail: [email protected].
Supported, in part, by grants T32 HD 07440, R01 HD 35631, and K24 HD01289 (to GM) from the National Institutes of Health.
Received March 27, 2003. Received in revised form July 23, 2003. Accepted August 15, 2003