Termination of pregnancy at less than 28 weeks of gestation and fetal weight less than 1000g is called miscarriage. There are two types of miscarriages: spontaneous and induced. Miscarriages that occur passively due to embryonic factors, maternal factors, paternal factors, environmental factors, etc. are spontaneous miscarriages. The specific causes are as follows: 1. Embryonic factors: The most common cause of spontaneous abortion, especially early spontaneous abortion (occurring before 12 weeks of gestation), is due to chromosomal abnormalities in the embryo (caused by infection, drugs) or chromosomal abnormalities in the aborting couple. Maternal factors: (1) systemic diseases; (2) genital malformations or abnormalities, such as uterine malformations, uterine fibroids, uterine adhesions, etc.; (3) endocrine abnormalities, such as luteal insufficiency, hyperprolactinemia, polycystic ovary syndrome, thyroid abnormalities, poorly controlled diabetes, etc.; (4) intense stress and bad habits, such as physical or mental trauma, excessive smoking and alcohol abuse, excessive (4) strong stress and bad habits, such as physical or mental trauma, excessive smoking and alcohol abuse, excessive drinking of coffee, heroin and other drugs; (5) abnormal immune function, etc. (3) paternal factors: such as systemic chronic wasting diseases, semen abnormalities, reproductive organ diseases, occupational factors, etc. (4) Environmental factors: such as excessive exposure to radiation and chemical substances such as arsenic, lead, formaldehyde, benzene, chloroprene, ethylene oxide, etc. In summary, there are many causes of spontaneous abortion, commonly caused by chromosomal abnormalities.