If the pregnancy is within ten weeks, any drop in the HCG in the blood indicates a miscarriage. If the HCG in the blood doubles between 1.7 and 2 days during this period, if it does not reach the normal doubling and there is a drop, it may be a difficult miscarriage, which may be caused by abnormal fetal development or embryonic arrest, or it may be caused by biochemical pregnancy or ectopic pregnancy. After the tenth week of pregnancy, it is normal for the HCG in the blood to increase more slowly and tend to decrease. It is normal for the HCG in the blood to decrease to 10% of the maximum value by the time of full-term delivery, so the decrease of HCG in the blood should be calculated according to the time of pregnancy.