Pregnancy is detected by measuring the concentration of human chorionic gonadotropin (hCG) in serum or urine. Human chorionic gonadotropin is a hormone produced by the placenta that supports the corpus luteum after fertilization of the ovum. Production of hCG begins at the time of implantation, and hCG can usually be detected in serum and urine within 10 days after fertilization. The level of hCG in serum and urine is usually above 25 mIU/mL, the cutoff for a positive pregnancy test, before the next expected period. Therefore, pregnancy can be detected reliably within two to three days following the first missed menses using a qualitative hCG test. In addition to diagnosis of pregnancy, the test is used in emergency departments to rule out pregnancy in circumstances in which x ray and other procedures are contraindicated by pregnancy. The test is also used to rule out pregnancy in females with acute abdominal pain that suggests the possibility of ectopic pregnancy (i.e., pregnancy outside the uterus).
Quantitative measurements of hCG are used as an aid to the diagnosis of ectopic pregnancy and trophoblastic tumors. Serial measurements may be used to monitor treatment and recurrence of tumors that secrete hCG. Measurement of hCG is also part of the triple marker screening procedure performed on maternal serum between weeks 15 to 20 to assess the fetal risk of Down syndrome.
Victoria DeMoranville, The Gale Group Inc., Gale, Detroit,