The hormone human chorionic gonadotropin (better known as hCG) is produced during pregnancy. It is made by cells formed in the placenta, which nourishes the egg after it has been fertilized and becomes attached to the uterine wall.
Levels can first be detected by a blood test about 11 days after conception and about 12-14 days after conception by a urine test. Typically, the hCG levels will double every 72 hours. The level will reach its peak in the first 8-11 weeks of pregnancy and then will decline and level off for the remainder of the pregnancy.
Human chorionic gonadotropin interacts with the LHCG receptor of the ovary and promotes the maintenance of the corpus luteum during the beginning of pregnancy. This allows the corpus luteum to secrete the hormone progesterone during the first trimester. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus.