Variability in the expression of trophectodermal markers beta-human chorionic gonadotrophin, human leukocyte antigen-G and pregnancy specific beta-1 glycoprotein by the human blastocyst

Improved culture conditions that support the development of human embryos t o the blastocyst stage in vitro led to the prospect of blastocyst transfer to increase pregnancy rates, Thus, there is a need for characterization of possible biochemical markers able to predict the implantation potential of human blastocysts, In this study, the expression of three placental markers that are expressed prior to implantation, beta-human chorionic gonadotroph in (HCG), human leukocyte antigen (HLA)-G and pregnancy specific beta-1 gly coprotein (SP-1), was investigated. beta-HCG transcript could be detected a s early as the two-cell stage, which is one to two cleavage divisions earli er than previously reported. Both beta-HCG and HLA-G transcripts could be d etected in the majority of blastocysts, but their levels were highly variab le. No association could be found between the amount of transcript for thes e genes, total cell number or cell death rate. Interestingly, there was a h ighly positive correlation between accumulation of beta-HCG and HLA-G trans cripts. SP-1 protein concentrations were assessed in the culture medium of blastocysts using enzyme-linked immunosorbent assay. There was a significan t positive correlation between SP-1 concentrations and blastocyst cell numb ers. Moreover, synthetic oviductal medium enriched with potassium resulted in an SP-1 concentration twice as high as that observed using human tubal f luid medium, These data suggest that SP-1 may be used to select blastocysts with higher cell number, possibly resulting in higher pregnancy rates.