Human chorionic gonadotropin (hCG)

A glycoprotein hormone produced in pregnancy that is made by the developing embryo and later by the syncytiotrophoblast of the placenta.

Composed of 244 amino acids and has a molecular mass of 36.7 kD.

Made up of an alpha and beta subunit.

The aplha subunit is identical to luteinizing hormone (LH), and follicle stimulating hormone (FSH) and thyroid stimulating hormone (TSH).

The beta subunit is unique to hCG.

The alpha subunit has 92 amino acids while the beta subunit has 145 amino acids.

HCG interacts with luteinizing hormone chorionic gonadotropin receptor and promotes maintenance of the corpus luteum allowing it to secrete progesterone.

Progesterone produced by the corpus lutein increases blood vessels which enables the sustenance of the growing fetus.

Theorized that hCG, with its highly negative charge, may repel immune cells of the mother and protect the fetus.

It prevents the disintegration of the corpus luteum of the ovary and maintains the production of progesterone necessary for progression of the pregnancy.

May affect immune tolerance in pregnancy.

A marker for gestational trophoblastic disease.

Measured in both the serum and urine.

Levels are monitored during pregnancy and when following germ cell tumors, and gestational trophoblast disease.

Laboratory analyses utilize a monoclonal antibody specific to the beta subunit of hCG, preventing

Monoclonal antibody tests prevents false positive tests by preventing confusing HCG with LH and FSH.

Highest levels in the morning.

Levels can be detected as low as 5mIU/mL.

In the absent of a visible fetus on ultrasound when beta hCG reaches the level of 1500 mIU/mL it is indicative of an ectopic pregnancy.

Pregnancy tests utilizing blood tests and the most sensitive urine tests usually detect hCG between 6-12 days after ovulation.

Gestational trophoblast disease or choriocarcinoma may produce high levels of beta-hCG.

HCG levels are a component of the triple test, a screening test for fetal chromosomal abnormalities.

HCG levels:

Three weeks since last menstrual period- 5-50 mIU/ml

Four weeks since last menstrual period-5-426 mIU/ml

Five weeks since the last menstrual period-18-7,340 mIU/ml

Six weeks since last menstrual period- 1080-56,500 mIU/ml

7-8 weeks since last menstrual period- 7650-229,000 mIU/ml

9-12 weeks since last menstrual period-25,700-288,000 mIU/ml

13-16 weeks since last menstrual period-13,300-254,000 mIU/ml

17-24 weeks since last menstrual period-4060-165,400 mIU/ml

25-40 weeks since last menstrual period-3640-117,000 mIU/ml

Non-pregnant females -less than 5 mIU/ml

Postmenopausal females -less than 9.5 mIU/ml

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