The human chorionic gonadotropin (hCG) test is done to check for the hormone hCG in blood or urine. Some hCG tests measure the exact amount and some just check to see if the hormone is present. HCG is made by the placenta during pregnancy. The hCG test can be used to see if a woman is pregnant or as part of a screening test for birth defects.

HCG may also be made abnormally by certain tumors, especially those that come from an egg or sperm (germ cell tumors). HCG levels are often tested in a woman who may have abnormal tissue growing in her uterus, a molar pregnancy, or a cancer in the uterus (choriocarcinoma) rather than a normal pregnancy. Several hCG tests may be done after a miscarriage to be sure a molar pregnancy is not present. In a man, hCG levels may be measured to help see whether he has cancer of the testicles .

HCG in pregnancy

An egg is normally fertilized by a sperm cell in a fallopian tube . Within 9 days after fertilization , the fertilized egg moves down the fallopian tube into the uterus and attaches (implants) to the uterine wall. Once the fertilized egg implants, the developing placenta begins releasing hCG into your blood. Some hCG also gets passed in your urine. HCG can be found in the blood before the first missed menstrual period, as early as 6 days after implantation.

HCG helps to maintain your pregnancy and affects the development of your baby (fetus). Levels of hCG increase steadily in the first 14 to 16 weeks following your last menstrual period (LMP), peak around the 14th week following your LMP, and then decrease gradually. The amount that hCG increases early in pregnancy can give information about your pregnancy and the health of your baby. Soon after delivery, hCG can no longer be found in your blood.

More hCG is released in a multiple pregnancy, such as twins or triplets, than in a single pregnancy. Less hCG is released if the fertilized egg implants in a place other than the uterus, such as in a fallopian tube. This is called an ectopic pregnancy.

HCG blood tests

HCG blood tests can be used to see if hCG is present but they can also measure the exact amount of hCG in the blood. A blood test can be used to see if a woman is pregnant, to check for abnormal pregnancies, or to test for hCG related to certain cancers.

The level of hCG in the blood is often used as part of a screening for birth defects in a maternal serum triple or quadruple screening test. Generally done between 15 and 20 weeks, these tests check the levels of three or four substances in a pregnant woman's blood. The triple screen checks alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and a type of estrogen (unconjugated estriol, or uE3). The quad screen checks these substances and the level of the hormone inhibin A. The levels of these substances—along with a woman's age and other factors—help the doctor estimate the chance that the baby may have certain problems or birth defects.

Pregnancy: Should I Have the Maternal Serum Triple or Quadruple Test?

In some cases a combination of screening tests is done in the first trimester to look for Down syndrome. This screening test uses an ultrasound measurement of the thickness of the skin at the back of the fetus's neck (nuchal translucency), plus a blood test of the levels of the pregnancy hormone hCG and a protein called pregnancy-associated plasma protein A (PAPP-A). This test is about as accurate as the second-trimester maternal serum quad screening.¹

HCG urine tests

HCG urine tests are usually used for routine pregnancy testing. The test does not measure the exact amount of hCG, but it shows if hCG is present. Home pregnancy tests that show hCG in urine are also widely available.