The partially purified pre-implantation suppressor factor may be one of several factors to play a role in successful pregnancy.

Embryo-associated immunosuppressor factor (EASF) is detected by its suppressive properties in the concanavalin A (ConA)-induced lymphocyte proliferation assay. EASF was partially purified from human embryo growth media of in vitro fertilized ova (pre-implantation EASF) as three fractions. The aim of the present study was to determine whether the EASF isolated from human embryo growth media is similar to the EASF secreted by the pre-embryo, which has been shown to be associated with successful pregnancy. EASF activity was measured in the purified pre-implantation EASF fractions and in a total of 24 individual embryo growth media obtained from 10 patients undergoing in vitro fertilization and embryo transfer, where 6 patients achieved successful pregnancy and 4 did not. The results show that: (i) all three EASF fractions and the individual embryo growth media from patients who became pregnant were suppressive when added to the early phase of ConA-supplemented cultures; this was not seen with the embryo growth media from patients who failed to become pregnant, suggesting that the purified pre-implantation EASF may be one of several factors responsible for successful pregnancy; and (ii) some embryo growth media, irrespective of the pregnancy outcome of the patient, showed an irreversible immunosuppressive effect on ConA-induced lymphocyte proliferation, whereas none of the purified EASF fractions did; this could be due to the loss of activity during purification.