Examinations
Examinations
Human Chorionic Gonadotropin (hCG) – Structure and Function
Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone with a molecular weight of 37.5 kDa.
- Consists of two subunits:
- Alpha-subunit: Non-specific, identical to LH, FSH, and TSH.
- Beta-subunit: Unique, with 145 amino acids, structurally similar to LH but with distinct biological functions.
Synthesis and Metabolism of hCG
- Primarily produced by the syncytial layer of trophoblast cells during pregnancy.
- Also secreted in low amounts by the pituitary gland.
- Metabolized in the liver; ~20% is excreted in urine.
Key Functions:
- Maintains corpus luteum activity (takes over from LH 6–8 days after ovulation).
- Primary pregnancy hormone, essential for early placental development.
- Levels double every ~1.5 days between weeks 2–5 of pregnancy.
- In multiple pregnancies, hCG levels are proportionally higher.
- Peaks at 10–11 weeks, then gradually declines.
- Stimulates ovarian production of estrogens and androgens.
- Supports placental and trophoblast tissue development.
- In men, stimulates testicular testosterone production.
- Avoid smoking for at least 30 minutes before testing.
- First- and second-trimester pregnancy monitoring
- Suspected trophoblastic disease (e.g., hydatidiform mole, choriocarcinoma)
- Suspected testicular malignancies in men
- Screening for fetal developmental abnormalities
Causes of Elevated hCG Levels
Pregnancy-Related Causes:
- Increased risk of Trisomy 21 (Down syndrome) in the first trimester
- Increased risk of fetal aneuploidy in the first and second trimesters
Non-Pregnancy-Related Causes:
- Choriocarcinoma
- Hydatidiform mole (molar pregnancy)
- Gestational trophoblastic tumor
- Testicular cancer
- Testicular trauma
- Breast cancer
Causes of Decreased hCG Levels
- Increased risk of Trisomy 18 (Edwards syndrome)
- False-negative results (e.g., testing too early, ectopic pregnancy with delayed hCG rise)