The predictive value of hCG β subunit levels in pregnancies achieved by in vitro fertilization and embryo transfer: an international collaborative study**Supported by the Foundation for Reproductive Medicine, Inc., Chicago, Illinois.††The International Investigators in collaboration for this study were Benjamin G. Brackett, M.D., Ph.D., The University of Georgia College of Veterinary Medicine, Atlanta, Georgia; Jairo Garcia, M.D., Suheil Muasher, M.D., Anibal A. Acosta, M.D., Mason C. Andrews, M.D., Gary Hodgen, Ph.D., Zev Rosenwaks, M.D., Georgeanna Seegar Jones, M.D., and Howard W. Jones, Jr., M.D., Eastern Virginia Medical School, Norfolk, Virginia; Robert H. Glass, M.D., Mary C. Martin, M.D., and Pramila Dandekar, M.Sc., University of California, San Francisco, California; Vesselko Grizelj, M.D., Ph.D., University Medical School of Zagreb, Zagreb, Yugoslavia; George Henry, M.D., Jon Van Blerkom, M.D., and Barbara J. Corn, R.N., Reproductive Genetics, In Vitro, P.C., Denver, Colorado; Aarne Koskimies, M.D., and Markku Seppälä, M.D., Helsinki University Central Hospital, Helsinki, Finland; David Magyar, M.D., Robert J. Sokol, M.D., and Patricia A. Rogus, R.N., Hutzel Hospital, Wayne State University, Detroit, Michigan; H. W. Michelmann, M.D., and L. Mettler, M.D., Universitats Frauenklinik, Kiel, German Federal Republic; Jean Parinaud, Ph.D., and Georges Pontonnier, M.D., Institut National de la Santé et de la Recherche Médicale, Toulouse, France; E. van Roosendaal, M.D., and R. Schoysman, M.D., Academisch Ziekenhuis Vrije Universiteit, Brussels, Belgium; Melvin Taymor, M.D., Beth Israel Hospital and Harvard Medical School, Boston, Massachusetts; Raimund Winter, M.D., Geburtshilflich-Gynakologische Universitatsklinik Graz, Graz, Austria; Richard J. Worley, M.D., and William R. Keye, Jr., M.D., University of Utah Medical Center, Salt Lake City, Utah; and John L. Yovich, F.R.A.C.O.G., University of Western Australia, Subiaco, Perth, Western Australia, Australia.‡‡Presented at The American College of Obstetricians and Gynecologists District VI Annual Meeting, September 25 to 28, 1985, Milwaukee, Wisconsin; the 41st Annual Meeting of The American Fertility Society, September 28 to October 2, 1985, Chicago, Illinois; and the 4th World Conference on In Vitro Fertilization, November 18 to 22, 1985, Melbourne, Victoria, Australia.