Bioactivity of human chorionic gonadotropin produced in frozen-thawed embryo transfer cycles with exogenous hormone replacement.

Human chorionic gonadotropin (HCG) is the glycoprotein hormone in pregnancy. It is known that hCG molecule has a variety of isoforms showing different potency in bioactivity. Taking advantage of rat Leydig cell assay to evaluate hCG bioactivity, we first tried to predict the prognosis of pregnancy in hormone replacement (HR)-cryopreserved embryo transfer cycles. There was no significant difference in serum estradiol (E2) level, immuno-hCG, or bioactive to immunoreactive hCG ratio (b/i) between normal pregnancies and miscarriages at 4 weeks of gestation. Linear regression did not show a significant correlation in E2 or b/i between normal pregnancies and miscarriages. The same analysis was performed on serum samples collected from spontaneously pregnant patients. In normal pregnancies b/i was significantly lower than that in miscarriages while serum E2 was significantly higher. The linear regression analysis was also performed to clarify the correlation between E2 and b/i, and no significant correlation was observed. To confirm the effect of E2 on hCG production, we treated trophoblastic cells with E2. E2 increased the immunoreactivity of hCG to a non-physiologically high concentration; however, it did not change its bioactivity, suggesting that E2 did not change hCG bioactivity by affecting trophoblasts directly. In this study, we presumed it possible to speculate the prognosis of the pregnancy in spontaneous cycles from b/i of hCG, but not in HR cycles. It is suggested that process of hCG secretion could undergo different endocrine regulations between the artificial sex steroid replacement cycles and spontaneous cycles with corpus luteum function.