Human Chorionic Gonadotropin (hCG)

Definition - What does Human Chorionic Gonadotropin (hCG) mean?

Human chorionic gonadotropin (hCG) is a hormone released by the placenta during pregnancy. Many pregnancy tests work by detecting hCG levels in the urine or blood, as hCG is normally only found in detectable levels only during pregnancy.

FertilitySmarts explains Human Chorionic Gonadotropin (hCG)

Human chorionic gonadotropin is released by the placenta during pregnancy to ensure that the uterus remains a hospitable environment for the developing fetus. hCG protects a pregnancy in the following ways:

  • The hormone interacts with the ovaries to encourage the release of progesterone, which stimulates the growth of thick uterine lining which is rich with blood vessels. These blood vessels are necessary to nurture the growing fetus.
  • The progesterone released by the ovaries in response to hCG also prevents uterine contractions, which occur in the absence of progesterone to squeeze uterine blood vessels shut and expel uterine material through menstruation.
  • Some scientists believe that hCG also plays a role in preventing the mother's immune system from rejecting the fetus, as the hormone has some properties which repel immune cells.
  • The timeline of hCG rise corresponds to the timeline of morning sickness experienced by many women. However, the mechanism by which hCG might cause morning sickness is unknown.

In a healthy pregnancy, hCG levels rise steadily throughout the first trimester. Around the beginning of the second trimester, hCG levels plateau and then begin to drop. Dropping hCG in the first trimester can indicate a problem with the health of the fetus or placenta. Three consecutive measurements showing falling hCG in the first trimester are ground for doctors to consider the probability that the fetus or placenta is not growing normally, and that miscarriage may occur soon.

hCG levels are also lower for ectopic pregnancies, in which a fetus begins to develop in the fallopian tube instead of in the uterus. Because of that, these life-threatening pregnancies may not show up on pregnancy tests. In cases where ectopic pregnancy is suspected but pregnancy tests are negative, ultrasound may be used to rule out fallopian tube abnormalities.

In rare cases, hCG may be produced by tumors arising from reproductive tissue. Because it can stimulate ovulation in women and the release of testosterone in men, hCG may also be administered as part of a fertility treatment.

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