Human chorionic gonadotropin (hCG) is a glycoprotein secreted by the placenta during pregnancy that consists of an alpha and beta subunit. The alpha subunit is structurally similar to the alpha subunits of FSH, LH and TSH. The beta subunit is distinct for hCG. The release of hCG into maternal circulation begins with embryo implantation 5 to 7 days after fertilization.. Maternal serum hCG peaks at 8–10 weeks and then declines to reach a plateau at 18–20 weeks (Fig. 6) of gestation and remains quiet constant until term. β-hCG lacks hCG activity, but several lines of study indicate that it exerts growth promoting activity.. Beta hCG database, levels chart, scatter plot and doubling time calculator by days after ovulation, IVF embryo transfer and missed period in early pregnancy.. HCG levels – 10 things you need to know . HCG levels – let’s face it, they’re hard to understand. You know the basics: HCG is the pregnancy hormone.. . .