1. From the Center for Perinatal Studies, Swedish Medical Center (C.Q., M.A.W., I.O.F., J.C.D.), Seattle; the Department of Epidemiology, University of Washington (C.Q., M.A.W.), Seattle; Clinical Research Division, Fred Hutchinson Cancer Research Center (W.M.L.), Seattle; and Obstetrix Medical Group (T.K.S., D.A.L.), Seattle, Wash.