Miscarriage is defined as the termination of a pregnancy in which the embryo or fetus is not yet viable. A miscarriage is defined as a termination of pregnancy at less than 28 weeks of gestation and weighing less than 1000g. Before 12 weeks, it is called early miscarriage, and between 12 and 28 weeks, it is called late miscarriage. Miscarriage is divided into spontaneous abortion and induced abortion, the rate of spontaneous abortion accounts for about 31%, of which 80% is early miscarriage, and 2/3 of early miscarriage is hidden miscarriage, which is now called biochemical pregnancy. There are many reasons for miscarriage, and 50%-60% of early miscarriages are related to chromosomal abnormalities of the embryo. In addition to the embryo itself, maternal factors, such as maternal systemic diseases and uterine malformations, reproductive tract abnormalities, endocrine abnormalities, such as luteal insufficiency, thyroid abnormalities, diabetes mellitus, poor blood sugar control, smoking and alcohol abuse, high fever and trauma, and immune function, as well as paternal factors, such as chromosomal abnormalities in some sperm, can also lead to spontaneous abortion. Other factors are environmental factors, too much exposure to radiation, harmful chemicals, can lead to miscarriage. Miscarriage is a natural elimination process, nature has a natural elimination process of the winners and losers, pregnancy also has to comply with this rule.