Human Chorionic Gonadotropin (hCG)

As you'll recall, we mentioned hCG when we studied what happens in the ovary after conception (Ovary/Post Conception.) That is, once fertilization takes place, the trophoblast layer of the developing blastocyst begins to produce and secrete hCG.

hCG, a protein hormone, begins to be produced in large amounts in early pregnancy. It is biologically similar to luteinizing hormone (LH). hCG's primary role is to keep the corpus luteum functioning, so that the corpus luteum continues to produce estrogen and progesterone.

hCG begins to decrease when the placenta is developed enough to become the major producer of these 2 hormones. However, it continues to be present until several weeks after pregnancy.

In addition to keeping the corpus luteum alive, hCG is thought to:

Detection of hCG is the basis of both laboratory and home pregnancy tests. The presence of hCG can be detected in the maternal serum 24-48 hours after implantation. It can be found in the maternal urine just a few days later.

The amount of hCG produced and secreted by the trophoblast layer increases, until it reaches a peak at about 8 weeks of pregnancy (120 to 130 IU/ml). It then decreases in amount, reaching a low at about 16 weeks (20-30 IU/ml), and remaining there for the rest of the pregnancy. Because hCG levels are low after 16 weeks, routine pregnancy tests performed after this time may be negative.

In high risk pregnancies, including those in danger of spontaneous abortion, hCG levels are monitored sequentially. The serum test is a radioimmunoassay of antibodies to a sub (beta) unit of hCG, or "beta hCG". Titers of beta hCG that do not rise rapidly in early pregnancy may signal lack of growth, or possible abortion.

The surge of hCG in early pregnancy is thought to be one of the causes of nausea, or morning sickness in pregnancy. Therefore, in the normal pregnancy, morning sickness early in pregnancy is thought to be associated with a more successful outcome. Since the nausea signals that an abundant amount of hCG is present, it is more likely there is an adequate supply of progesterone to prevent spontaneous abortion.

On the other hand, abnormally severe morning sickness may necessitate investigation for multiple pregnancy, or hydatidiform molar pregnancy. hCG levels are higher with multiple gestation (more trophoblast tissue produced) and hydatidiform molar pregnancies (which feature an aberrant growth of trophoblast tissue). Molar pregnancies can be associated with development of malignancies, and should be carefully followed up.

Please explore the interactive learning tool below. Be sure to click on the buttons indicating days after fertilization ("day 6") and the "Next" and "Prev" buttons. Though you won't be "responsible" for it's material, it is really a picturesque version of the material that was just presented. Text of the course continues after diagram.


Please go to to download the Flash plug-in

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One of the functions of hCG is to stimulate fetal testosterone production.


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