PROBLEM and METHOD: Early pregnancy factor (EPF), an Immunosuppressive substance, which appears in pregnant women's sera 48 h after fertilization, is a kind of pregnancy‐specific protein. To determine whether the EPF activity could be a super early indicator of pregnancy, we used rosette inhibition assay to detect EPF activity in the sera, collected from 70 women 2–7 days after ovulation intending to conceive monitored by ultrasonography. Simultaneously we selected 40 non‐pregnant sera and 12 early‐pregnant sera as negative control and positive control, respectively. RESULTS: The results of this study demonstrated that EPF activity is detected in 35 women's sera out of 70 women within 2–7 days after ovulation, and 28 women out of the 35 were pregnant, which was known by follow‐up, and 7 were not pregnant, possibly due to either false positive results or embryo loss because of preimplantation failure, thus causing no pregnancy. The other 35 out of 70 had no EPF activity and 34 of them were not pregnant, which was known by follow‐up, but one case became pregnant, which was false negative result. Our study showed that diagnosis of the super early pregnancy could be made by detecting EPF activity in maternal serum within the time of preimplantation. The accuracy of pregnancy diagnosis by this method is 88.6%, with a false negative rate of 3.4% and a false positive rate of 17.1%. The β‐HCG level was measured from the above 70 women's sera in order to contrast EPF activity. All of the sera collected 2–6 days following ovulation indicated that there were lower β‐HCG values in very early pregnancy (≥a5 mIU/ml). On the seventh day after ovulation, EPF activity was detected in 11 out of 15 sera with only 2 of them with a b‐HCG level that reached or slightly surpassed that of the early pregnancy diagnosis (5 mIU/ml and 5.4 mIU/ml, respectively). This demonstrated that β‐HCG is not the earliest signal of pregnancy; otherwise the EPF activity is one that appears 2–6 days earlier than β‐HCG appears. We measured the progesterone level of the 48 sera from the 70 collected above within 2–7 days postovulation and found most of them reached the level of progesterone in the luteal phase (7.5–98.3 nmol/L). This indicated that ovulation had taken place in these women, which was in accordance with observations by ultrasonography. CONCLUSIONS: Our study showed that diagnosis (of 88.6%) of super early pregnancy could be made with an accuracy of 88.6% by detecting EPF activity in maternal serum within 2‐days after ovulation. This offers a basis for pregnancy diagnosis for the women who attempt to terminate their pregnancy safely or who conceive unexpectedly, and it contributes to family‐planning.

PROBLEM: To detect whether or not the early pregnancy factor (EPF)‐like activity, or chaperonin 10, could be in the sera of patients with trophoblastic tumor in order to find another more efficient means to diagnose this kind of tumor. METHOD OF STUDY: The rosette inhibition assay was used to detect EPF‐like activity in 216 sera, collected from patients with gestational trophoblastic tumor, including 47 sera of patients with choriocarcinoma, 68 sera of patients bearing invasive mole, and 101 sera of patients with vesicular mole. RESULTS: The accuracy of diagnosing malignant trophoblastic tumor by detecting EPF‐like activity is 91.3% (105/115), with a false positive rate of 14.58% and a false negative rate of 4.48% by this method. Furthermore, the rosette inhibition titer (RIT) values have significant difference (P < 0.001) between the sera in patients with malignant trophoblastic tumor before treatment and those after treatment. CONCLUSIONS: This study demonstrated that diagnosis of malignant trophoblastic tumor could be made with an accuracy of 91.3%) by detecting EPF‐like activity and that EPF‐like activity could be used as an indicator to distinguish benign from malignant trophoblastic tumor.