What is Human Chorionic Gonadotropin or hCG?

Human chorionic gonadotropin, commonly known as hCG, is a hormone found in women's blood and urine throughout pregnancy. The hCG becomes detectable in blood shortly after the time the pregnancy implants in the uterus (roughly three weeks into a four-week menstrual cycle). The hCG becomes detectable in the urine around the time of the first day of a missed menstrual period; home pregnancy tests work by detecting hCG in the urine.

In early pregnancy, the detectable levels of hCG should double roughly every two days. Slower rising or falling hCG levels can be a clue to impending miscarriage.

Women whose hCG level falls over a period of two to three days in the first trimester in two quantitative hCG blood tests are often advised that this means an impending miscarriage. This is especially true for women with other miscarriage symptoms, such as vaginal bleeding during pregnancy.

Decreasing hCG levels later in pregnancy, such as the second and third trimester, are probably not a cause for concern. Most doctors do not check serial quantitative hCG levels for purposes of evaluating the progress of a pregnancy after the first trimester, although single hCG levels might be checked as a part of the AFP prenatal screening test.

hCG levels can vary dramatically, from woman to woman and from pregnancy to pregnancy. Generally, an hCG level of less than 5 mIU/ml means a woman is not pregnant and anything above 25 mIU/ml indicates a pregnancy has occurred.

While the below ranges give an idea of what is considered normal, the results of one hCG blood test mean very little. Rather, the change in the level between two consecutive tests done two to three days apart is much more telling of how a pregnancy may progress.

In early pregnancy, doctors might use one of two types of blood tests to check a woman’s levels of hCG, a pregnancy hormone. The most common is a quantitative hCG blood test, which evaluates the level of hCG in the woman’s blood and returns a number, with the measurement unit being mIU/mL, or milli-international units (thousandths of international units) of hCG per milliliter of blood.

Quantitative hCG blood tests provide highly useful information about women having miscarriage symptoms in the first few weeks after conception. Comparing levels from two quantitative hCG blood tests to look at the hCG doubling time over two to three days can give a strong indication of whether or not the pregnancy is progressing as it should be at that point in time, helping a doctor make a proper assessment.

Doctors may also use qualitative hCG blood tests, which merely return a yes or no answer on whether or not the woman has hCG in her blood.