1. Department of Obstetrics and Gynecology (S.F.B., E.W.F., K.Q., H.L.), Philadelphia, Pennsylvania 19104
2. Center for Clinical Epidemiology and Biostatistics (S.F.B., M.D.S., T.R.R.), Philadelphia, Pennsylvania 19104
3. Abramson Cancer Center (T.R.R.), Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104