Human chorionic gonadotropin, or hCG, is a hormone produced by the placenta during a normal pregnancy. Simple home test kits, which detect the presence of hCG in urine, are effective soon after the pregnancy's conception. To learn the actual amount of hCG in the bloodstream, health professionals must test a blood sample. The results may indicate pregnancy progress or problems, cancer and other conditions.
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During a normal pregnancy, a sperm fertilizes an egg, usually in one of the two fallopian tubes leading from the ovary to the uterus. The fertilized egg then travels the rest of the way down the tube and attaches inside the uterus. Here, a placenta develops and begins releasing hCG to maintain the pregnancy and help the fertilized egg develop. A blood pregnancy test may reveal hCG levels as early as six days after the fertilized egg implants, and a urine test may diagnose a pregnancy mere days after a woman's first missed menstrual period. Blood levels of hCG continue to increase through the first trimester, slightly decline over the next two trimesters, then disappear altogether after the baby is born.
A woman with abnormally high hCG levels may be carrying twins or multiples, or she may be further along in her pregnancy than previously believed. In combination with a lower maternal serum alpha-fetoprotein level, an abnormally high hCG level may indicate the baby has Down syndrome. Very high levels of hCG sometimes indicate a type of gestational trophoblastic disease called a molar pregnancy. In a normal pregnancy, the placenta feeds the fetus. In a molar pregnancy, the tissue that is supposed to develop into the placenta instead overdevelops into an abnormal mass of cells, called a hydatidiform mole. In a complete molar pregnancy, there exists the abnormal placental tissue but no fetus; in a partial molar pregnancy, some fetal development accompanies the abnormal mass of tissue.
Unless a woman is earlier in her pregnancy than believed, low hCG levels usually indicate a troubled or terminated pregnancy. According to MedlinePlus, hCG levels should almost double every two days during early pregnancy. Abnormally low levels may result from an ectopic pregnancy, where the fertilized egg implants outside of the uterus; a threatened or incomplete miscarriage; or fetal death. In very early pregnancy, when hCG levels are still low, the pregnancy may test positive one day, and then negative a few days later, due to natural termination of the pregnancy. Up to 50 percent of all conceptions terminate in this manner.
Certain cancer tumors originating from an egg or sperm -- called germ cell tumors -- may abnormally raise hCG levels in men and non-pregnant women. Choriocarcinoma, or cancer of the uterus, may produce the chemical, as may cancer in a man's testicles. Other cancers that may raise hCG levels include certain cancers of the stomach, liver, lung, pancreas and large intestine.
A urine test performed early in a pregnancy or late in the day may fail to detect levels of hCG, producing a false negative pregnancy test result. Also, hormone levels may remain elevated up to four months after a miscarriage or abortion. In some cases, women receive injections of hCG to treat infertility, which may artificially raise blood hCG levels for several days after the injection. According to Stanford Medicine, marijuana use may raise hCG levels. Some prescribed medications that also may affect readings include the anticoagulant heparin, as well as some diuretics, hypnotics, antipsychotics and anti-nausea medicines.