[Detection of early pregnancy factor in the sera of conceived women before nidation].

In order to apply the early pregnancy factor (EPF) to early diagnosis of fertilization, the establishment of optimal conditions for assay of EPF was attempted, and then EPF in the sera of contracepted and conceived women 4 to 6 days after ovulation were measured. For assay of EPF, 0.25 ml of 1:2 step diluted anti-human lymphocyte serum (ALS), 0.05ml of guinea pig serum as complement and 0.1ml of lymphocytes suspension (1 X 10(7)/ml) pretreated with test serum were mixed and then incubated at 37 degrees C for 90 min. To this mixture 0.1ml of sheep red blood cell suspension (2 X 10(9)/ml) was added and the rosette formation was counted after centrifugation. The rosette inhibition titer (RIT) was expressed as reciprocal of ALS dilutions which resulted in less than 75% of rosette formation as compared with the control. RITs of the conceived women who were assayed on the 5 th day after ovulation were in the range from 16 to 32 X 10(3), while that of the control contraceptive women who were assayed on the same day was in the range from 2 to 4 X 10(3). The sterile women who received AIH but failed to conceive all showed less than 4 X 10(3) as RIT. These results suggest that the assay of EPF is valuable in detecting the early stage of fertilization and possibly may help to differentiate the impairment of embryo implantation from non-fertilization of the ovum as a cause of sterility.