HCG is a glycoprotein hormone with a molecular weight of 46 kDa which is naturally secreted by placenta during pregnancy. This hormone is formed by two chains, namely alpha and beta. Alfa chain has a structure similar to those of other LH, TSH and FSH glycoprotein hormones. Level of this hormone in the blood increases rapidly with the onset of pregnancy and it reaches the highest level at the end of the first three months. This hormone can be evaluated within 8 to 11 days after fertilization (it reaches to an approximate level of 5 IU/L). HCG level is almost twice in twin pregnancies and it is unusually low in anomalies such as ectopic pregnancies and spontaneous abortions. One of the most important uses of BHCG measurement is the early diagnosis of pregnancy. In addition, it is a suitable index for diagnosing and treating trophoblastic tumors, germinal tumors and testicle.