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Shortly after implantation of a fertilized ovum in the uterine lining, HCG begins to be produced.
Levels of HCG approximately double every 2-3 days in a normal pregnancy.
By the time of the first missed menstrual period, pregnancy tests are usually positive (with a sensitivity of 30-35 mIU/ml).
Quantitative HCG measurements can be useful in evaluating threatened abortions.
Doubling every 2-3 days is reassuring.
More slowly rising levels are equivocal.
Plateau levels or falling levels are non-reassuring.
They may also be useful in evaluating possible ectopic pregnancy.
With > 1500 units of HCG, a normal intrauterine pregnancy is usually seen with transvaginal ultrasound.
This threshold, also known as the "discriminatory zone" may range from 1,000 to 2,000 units of HCG, depending on the lab, the ultrasound equipment and the sonographer's experience.
Elevations caused by:
Pregnancy
Gestational Trophoblastic Disease
Decreases caused by:
Miscarriage (spontaneous or induced)
Following obstetrical delivery
With resolution of an ectopic pregnancy
Following effective treatment of gestational trophoblastic disease
