Recurrent miscarriage is defined as 2 or more spontaneous miscarriages, also known as habitual miscarriage. There are many causes of recurrent miscarriage, which are often divided into the following areas: First: genetic factors. Chromosomal abnormalities are common causes, including chromosomal abnormalities in both spouses. Half of the fetuses with spontaneous abortions have chromosomal abnormalities. Second: endocrine factors. Luteal insufficiency is a common cause. Luteal insufficiency is manifested by insufficient production of progesterone or insufficient duration of corpus luteum. Patients with diabetes mellitus, polycystic ovary syndrome and endometriosis have a high rate of miscarriage due to endocrine disorders. Third: anatomical factors. Uterine cavity abnormalities and cervical insufficiency can lead to miscarriage. Uterine abnormalities include uterine malformations, uterine adhesions and submucosal fibroids, polyps, etc. Fourth: immune factors. Pregnancy requires maternal and infant immune compatibility, and a normal pregnancy is a successful semi-identical transplant. Lack of blocking antibodies and the presence of autoantibodies (such as anticardiolipin antibodies, lupus anticoagulation factor, and antisperm antibodies) can lead to miscarriage. Fifth: Self-disease. Multiple microbial infections, immune system diseases, etc. Sixth: environmental factors. Ionizing radiation, bad living habits, exposure to toxic substances, etc. Seventh: Unknown cause. The existing medical level cannot detect the cause.