When pregnancy ends before 20 weeks and the fetus weighs less than 500 grams, it is called miscarriage. Miscarriage can be divided into spontaneous abortion and artificial abortion; artificial abortion is the termination of pregnancy by artificial or drug methods, which is called early pregnancy termination. Spontaneous abortion refers to the embryo or fetus being automatically separated from the mother and expelled for some reason before 28 weeks of pregnancy, and its incidence rate is about 15% to 20%. Spontaneous abortion occurs 3 or more times in a row and occurs within three months of pregnancy, which is also called recurrent early spontaneous abortion. At the same time, spontaneous abortion also has a kind of missed abortion, which refers to the embryo or fetus that has not been naturally expelled after 2 months of intrauterine death. The causes of spontaneous abortion are very complicated, including chromosomal abnormalities, abnormal fertilized eggs, poor embryo quality, poor egg quality due to old age, poor sperm quality due to old age, genetic diseases, environmental pollution, etc.