Human chorionic gonadotropin (hCG) is an amazing hormone that can signal the wondrous start of pregnancy or warn of the growth of a dangerous tumor. HCG can be detected in either blood or urine. Pharmaceutical preparations of hCG have been misused as a diet aid.
Molecular Structure of hCG
HCG is a hormone made up of two smaller molecular parts, named alpha and beta subunits. The alpha subunit is identical to the alpha subunit of two other hormones, luteinizing hormone (LH) and thyroid hormone. The beta subunit of hCG is the molecule detected by pregnancy tests because it is unique to hCG.
Significance
Human embryos produce hCG during implantation into the uterus. HCG produced by the embryo enters the blood stream and urine as early as 10 days after implantation. If the embryo implants in the wrong place (for instance, the Fallopian tubes), the embryo makes hCG, but levels are lower and don't double every other day as expected for normal pregnancies.
HCG production can also signal the presence of specific tumor types such as nonseminomatous germ cell (testicular) tumors and hydatiform mole and choriocarcinoma (abnormal embryo implantation tumors).
Pregnancy Tests
Pregnancy tests look for the hCG molecule in either urine or blood. The urine test for hCG is a qualitative test, meaning the color result indicates whether or not hCG is detected. The blood test for hCG is quantitative meaning that a number for the concentration of hCG, not just a color result, is generated. False negative results can happen with the urine test if the test is performed too early in the pregnancy before enough hCG is produced or if the urine is too dilute. HCG tests are usually repeated to be sure of the pregnancy result.
Time Frame during Pregnancy
According to a physician reference websitethe Family Practice Notebook, during early pregnancy (weeks four to eight), hCG levels in the blood double every 48 to 72 hours from around 100 mIU/ml. When the gestational sac is visible by ultrasound at around five weeks, hCG blood levels range from 1,800 to 3,500 mIU/ml. By the time cardiac activity is visible on ultrasound (usually by seven weeks), hCG levels are typically around 20,000 mIU/ml. After 20 weeks of pregnancy, hCG levels peak and level out. In the first trimester, after eight weeks, hCG levels range between 30,000 and 100,000 mIU/ml. By the second trimester, levels have peaked and decreased to a range of 10,000 to 30,000 mIU/ml. By the third trimester, normal levels range between 5,000 and15,000 mIU/ml.
HCG Produced by Tumors
Implantation of embryos derived from abnormally fertilized eggs can create tumors called choriocarcinomas, which produce huge amounts of hCG, sometimes exceeding 1 million IU/ml.
Men normally never secrete hCG. When hCG is detected in the blood or urine of men, it can signal the presence of a type of testicular cancer called nonseminomatous germ cell tumor.
Misconceptions
HCG has been promoted by some who claim that hGC injections can cause the body to preferentially burn fat and quiet hunger pangs. Over 50 years ago, Dr. Albert T. Simeons first promoted a new diet plan consisting of injecting hCG and eating only 500 calories a day. In 1976. The Federal Trade Commission (FTC) ordered the Simeons Corporation to stop claiming that this diet plan was safe, effective and approved by the FDA since no scientific evidence existed to support these claims. In 1975, the FDA required manufacturers of hCG to place a warning label on vials of hCG stating that the use of hCG for weight loss is not supported by scientific data.
