Human Chorionic Gonadotrophin (HCG)
Definition: A glycoprotein secreted by syncytiotrophoblast.
Production: It starts at implantation (7 days after fertilization) and its levels double every 2 days till it peaks at around 10weeks gestational age (1,000,000 Units). After the peak, level decreases as the pregnancy progresses to full term.
Detection: By urine analysis (Standard pregnancy test), or by measuring the beta subunit of HCG in serum (More sensitive and specific).
Uses of HCG:
Diagnosis of pregnancy: Appears in the urine 8 days after fertilization.
Diagnosis and follow up of some ovarian and trophoblastic tumors.
Evaluation of threatened abortion: If levels are doubling every 2 days, pregnancy is still intact. If no doubling, suspect missed abortion. Explained in detail later.
Functions of HCG:
Maintains corpus luteum until placental function is well established. (10weeks).
Stimulates fetal testicular function in utero if the fetus is male.