Miscarriage in a natural state, i.e. not caused by artificial purposes, is called spontaneous miscarriage. Miscarriage occurring before 12 weeks is called early miscarriage, and miscarriage from 12 weeks to less than 28 weeks of gestation is defined as late miscarriage. There are many causes of spontaneous miscarriage: i. Genetic factors, chromosomal abnormalities, including chromosomal abnormalities in couples and chromosomal abnormalities in embryos. Common chromosomal abnormalities in couples are balanced translocation and Robertson translocation, etc. Second, maternal endocrine disorders, manifested as luteal insufficiency, polycystic ovary syndrome, hyperprolactinemia, thyroid disease, and diabetes mellitus may be the cause of spontaneous abortion. Third, abnormalities of the maternal reproductive tract. It mainly includes uterine anomalies such as unicornuate uterus, bicornuate uterus, double uterus and uterine longitudinal septum. Post-abortion syndrome, uterine adhesions, uterine cavity volume reduction, cervical insufficiency causing late abortion and preterm delivery are the main causes of miscarriage in the middle of pregnancy. In addition, uterine fibroids submucosal fibroids and myxoma greater than 5 cm are associated with miscarriage. IV. Systemic diseases of the mother, such as severe infections, hyperthermic diseases, severe anemia or heart failure, thrombotic diseases, chronic wasting diseases, chronic liver and kidney diseases or hypertension, may lead to miscarriage. tORCH infection, although it has little effect on pregnant women, can infect the fetus leading to miscarriage. V. Other, including unhealthy lifestyle, such as alcoholism, excessive caffeine consumption and environmental factors may lead to miscarriage.