Human Chorionic Gonadotropin is a hormone produced by the chorion of the placenta. It consists of two subunits: the a-subunit and the b-subunit. The a-subunit is essentially identical to and shared with FSH, TSH and LH while the b-subunit is characteristic for HCG. Human Chorionic Gonadotropin supports and maintains the corpus luteum in the early stage of pregnancy (from 8-10 week).

 If the implantation of the fertilized egg cell occurs, which takes place between 6 and 8 day after ovulation, 48 hours later there is a detectable level of HCG in the blood (> 1 mIU/ml). However, because there is a possibility of a spontaneous micro-abortion, it is only the level > 5 mIU/ml (and for some women even > 25 mIU/ml) which is regarded as indicative of pregnancy.

HCG is also detectable in urine and this is what home pregnancy tests base on. The technology used in the production of the latest generation of pregnancy tests uses monoclonal HCG beta antibodies. As a result, the produced tests are very sensitive and effective. In case of urine pregnancy tests currently available on the market, the results may appear even 3-4 days after the implantation of the fertilized egg cell and after 6-7 days (the time of the expected period) 98% of results will be positive. If  a test is done 1 week after the expected period and there is a positive result, the woman can be certain she is pregnant.

 HCG levels peak at about 8-10 weeks of pregnancy and then declines, remaining at lower levels until the end of pregnancy.
There is a large variation in the norms of HCG levels at different stages of pregnancy, calculated from the first day of the last period.

 Sample variables

Weeks of pregnancy – the level of beta HCG
3 - 5-50 mIU/ml
4 - 5-430 mIU/ml
5 - 19-7340 mIU/ml
6 - 1000-56000 mIU/ml

More precise level ranges can be obtained when the date of ovulation is known.

In the evaluation of early pregnancy, the rise in HCG over time is more important than its absolute values.   A healthy pregnancy is characterized by a HCG rise of at least 66 % within 48 hours and 114 % within 72 hours. The more advanced the pregnancy the slower the rise of HCG concentration. In the range 1200 mIU/ml-6000 mIU/ml the level of HCG typically doubles in 96 hours(4 days), and in case of concentrations over 6000 mIU/ml this time can be even longer. When the level of HCG exceeds 6000 mIU/ml, the state and localization of pregnancy can be better evaluated by means of USG. Abnormal HCG values may indicate the threat of miscarriage or ectopic pregnancy (the rise is slower than the normal one). A temporary decline in the level of HCG is possible, however, in cases when there are two embryos implanted in the uterus (which happens in multiple ovulation or after In Vitro fertilization) and one of them atrophies. It does not, however, affect the successful course of pregnancy.