In normal pregnancy, after the fertilized egg is laid, human chorionic gonadotropin starts to be secreted due to the formation of fertilized egg trophoblast, i.e. hcg. About 3 weeks after menopause, hcg can be measured in peripheral blood, and the doubling situation at this time is about 1.7-2.0 times of increase. The general judgment is based on 6 weeks, hcg should be 10,000mIU/ml at 6 weeks of pregnancy, if it is still less than 10,000mIU/ml at 6 weeks, that is, hcg is low. However, the doubling of hcg varies from person to person, the doubling is faster in the early stage and slower in the late stage. Under normal circumstances, if the hcg is 2000mIU/ml on the first day, it should be 4000mIU/ml on the third day by the same laboratory, and 8000mIU/ml on the fifth day by the same laboratory. this doubling situation reaches its peak at the 8th week of pregnancy, after which the hcg level gradually decreases.