1. Department of Obstetrics and Gynecology; Tokyo University Branch Hospital; Bunkyo-ku Tokyo 112 Japan
2. Iatron Laboratories, Inc.; Chiyoda-ku Tokyo 101 Japan
3. Department of Epidemiology; The National Institute of Health; Shinjuku-ku Tokyo 162 Japan
4. Department of Obstetrics and Gynecology, Faculty of Medicine; The University of Tokyo; Bunkyo-ku Tokyo 113 Japan