Human chorionic gonadotropin (hCG) is a glycoprotein hormone produced by placenta after conception. hCG is comprised of a ? subunit with 92 amino acids and a ? subunit with 245 amino acids. The ? subunit is identical to that of LH (Luteinizing hormone), FSH (Follicle-stimulating hormone) and TSH (Thyroid-stimulating hormone). hCG sustains corpus luteum, stimulats progesterone secretion, hence is critical to early foetus development. It has also been reported that hCG plays a role in the development of foetus’s tolerance to maternal immunity. hCG is the most sensitive biomarker for pregnancy.