Human chorionic gonadotropin, or hCG, is a natural hormone made in the body in significant levels only during pregnancy. During pregnancy, levels of hCG can be measured in home urine tests, or by blood tests. At most other times, blood levels of hCG are only about 2 milli-International units per milliliter (mIU/ml).
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Role of hCG
After fertilization, the egg begins to divide, creating more cells. The cells differentiate into those that will form the actual embryo, and the surrounding cells that will become the embryo’s contribution to the placenta. The surrounding cells produce hCG, whose job is to facilitate the embryo’s implantation into the uterus, and to tell the maternal ovaries to keep producing the progesterone needed for the pregnancy to continue.
By as early as the 11th day after fertilization, embryonic cells make significant levels of hCG, enough for detection in the blood. This is equivalent to between 3 to 4 weeks since the last menstrual period. The simplest blood tests are qualitative, asking only if hCG is present in the blood or not. If hCG is detected, the woman is pregnant. Quantitative tests measure the actual amount present in the blood. A result with hCG levels of less than 5 mIU/ml means not pregnant, and any level higher than 25 mIU/ml indicates pregnancy. Once an hCG result indicates pregnancy, doctors do not continue to check levels unless they suspect a problem, such as an ectopic pregnancy or a molar pregnancy.
After an ectopic pregnancy or miscarriage, doctors usually continue to check hCG levels until they return to pre-pregnancy levels to be sure that all of the embryonic cells have left the woman’s body. According to the American Pregnancy Association, levels of hCG generally return to pre-pregnancy levels about 4 to 6 weeks after the pregnancy loss, although the timing can vary with the circumstances of the loss.
Some conditions other than pregnancy can cause higher than normal levels of hCG in the blood. Although the exact molecular structure of hCG made by a woman’s body differs from that made by embryonic cells, it can be measured using the same tests. During normal menopause, levels of hCG typically rise to about 10 mIU/ml. Some forms of cancer, including breast and uterine cancer among others, can increase hCG levels. Cirrhosis of the liver, inflammatory bowel disease, and an ulcer in the duodenum can also increase hCG levels in the blood.
Sometimes doctors treat infertile women with hCG, in combination with other drugs, to encourage ovulation. Infertile women treated with hCG can have detectable levels of hCG in their blood even if they are not pregnant. Her doctor will have to take care in interpreting the results of an hCG test in the event of a possible pregnancy.