The beta-hCG subunit is present in the syncytial layer of the blastomere. Hyperglycosylated hCG is a form of hCG produced by invasive cytotrophoblast cells in early pregnancy and implantation. hCG messenger RNA is detectable in the blastomeres of 6- to 8-cell embryos at 2 days but cannot be isolated in culture medium until 6 days. Detection in maternal serum and urine is evident only after implantation and vascular communication has been established with the decidua by the syncytiotrophoblast 8-10 days after conception.