From the Department of Medical Epidemiology (S.C., B.C., A.E., G.P., F.G.) and the Department of Laboratory Science and Technique (A.R.), Karolinska Institute, Stockholm, Sweden; the International Epidemiology Institute, Rockville, Md. (L.B.S., W.J.B., J.K.M.); and the Department of Genetics and Pathology (G.A.) and the Department of Women's and Children's Health (B.C., E.L.), Uppsala University, Uppsala, Sweden.
Address reprint requests to Dr. Cnattingius at the Department of Medical Epidemiology, P.O. Box 281, Karolinska Institute, SE-171 77 Stockholm, Sweden.