Chorionic gonadotropin (hCG) is a hormone produced by the placenta during pregnancy. The function of hCG in the body is to support the synthesis of progesterone in the corpus luteum during the first weeks of pregnancy until progesterone is produced by the placenta.
hCG testing is used for the early detection of pregnancy. Blood levels of hCG in pregnant women are >30 mIU/ml. A result between 5 and 25 mIU/ml is considered inconclusive in a confirmatory pregnancy study and should be repeated after a few days.
Men and non-pregnant women have hCG levels of <5 mIU/ml.
In a normal pregnancy, hCG appears in the blood 5-7 days after fertilisation. During the first trimester of pregnancy, hCG levels rise very rapidly (doubling every 48 to 72 hours), reaching peak concentrations around weeks 7-11 of pregnancy (up to 300,000 mIU/ml). During the last trimester of pregnancy, hCG levels fall from the maximum to around a quarter and remain stable until delivery. After delivery, hCG levels fall to pre-pregnancy levels (<5 mIU/ml) within 2 to 3 weeks. If hCG levels do not fall to pre-pregnancy levels 3 weeks after delivery, placental retention in the uterus may be the cause. hCG testing is also used to detect ectopic pregnancy and assess the risk of foetal malformations.