The decrease in HCG is caused by insufficient secretion of trophoblast cells after pregnancy, which indicates the possibility of preterm miscarriage. The decrease in HCG secretion by trophoblast cells is related to chromosomal disorders of the embryo, maternal diseases, ectopic pregnancy, etc. It is recommended to go to the hospital for examination in time, and depending on the details of the examination, the fetus can be treated by supplementing with human chorionic gonadotropin, a glycoprotein secreted by the trophoblast cells of the placenta, which can maintain the life of the menstrual corpus luteum. If the corpus luteum is insufficient, it may lead to miscarriage in early pregnancy. It is recommended to monitor pregnancy regularly after pregnancy to prevent miscarriage.