Human chorionic gonadotropin (HCG) consists of two subunits: alpha and beta. The alpha subunit is the same in pituitary hormones such as luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). The beta subunit (beta-HCG) is used for immunometric determination of the hormone. The level of beta-HCG in the blood as early as 6-8 days after conception allows for the diagnosis of pregnancy (its concentration in the urine reaches the diagnostic level 1-2 days later than in the blood serum).