Detection of an immunosuppressive factor in human preimplantation embryo cultures

Within 48 hours of fertilization of human preovulatory oocytes in vitro, an immunosuppressive factor was detected in the culture medium by a rosette inhibition test. Cultures in which fertilization of the oocyte was unsuccessful were indistinguishable from control medium. Release of an early pregnancy factor from the preimplantation embryo could be of clinical significance to the establishment of pregnancy after embryo transfer.