Choriocarcinoma-like human chorionic gonadotrophin (HCG) and HCG bioactivity during the first trimester of pregnancy

The objective of this study was to evaluate the distribution of choriocarcinoma-like human chorionic gonadotrophin (HCG) isoforms during first trimester pregnancy and their relationship with in-vitro HCG bioactivity. This was done by means of a retrospective analysis of patients' sera with first trimester normal intrauterine and abnormal (ectopic) pregnancies. Serum samples were obtained from 38 women with an amenorrhoea of <10 weeks. From these, 19 had a normal intrauterine pregnancy (IUP) and 19 an ectopic pregnancy (EP). Total immunoreactive HCG (HCGi), free beta-HCGi and oestradiol were measured by enzyme immunoassays and bioactive HCG by the mouse Leydig cell bioassay. The alterations in HCG isoform content were measured by the combination of two immunometric assays, B152 for choriocarcinoma-like HCG and B109 for intact HCG detection and expressed as the B152/B109 ratio. Choriocarcinoma-like HCG isoforms ratio measured by B152 and B109 assays was significantly higher in the low subgroups of free beta-HCGi and gestational age (P = 0.0111 and 0.0036 respectively). Whereas bioactive to immunoreactive HCG ratios (b/i ratio) were significantly higher when free beta-HCGi concentrations were low (P = 0.0010), no correlation was found between the variation of bioactivity (b/i ratio) and the proportion of choriocarcinoma-like HCG isoforms (B159/B108). It is concluded that in first trimester pregnancies (i) the modulation of HCG in-vitro bioactivity is not related to the variation of choriocarcinoma-like HCG isoforms secretion and (ii) the amount of choriocarcinoma-like HCG isoforms secreted by the early trophoblast is predominant and may be the result of an early developmental regulation of glycosylation enzyme.