Recurrent miscarriage is defined as 3 or more consecutive spontaneous abortions with the same sexual partner. Most experts believe that 2 consecutive miscarriages should be taken seriously. Recurrent abortion is one of the main causes of fertility failure in women of childbearing age. Statistics from different regions, classes and ages show that about 5% of women of childbearing age have 2 or more miscarriages and 1%-2% have 3 or more miscarriages, and the risk of recurrence increases with the number of miscarriages. The causes of recurrent miscarriage are complex and varied, and lack of specific clinical manifestations. Most patients have multiple causative factors at the same time, and if the screening program is not comprehensive and appropriate treatment is not given in time, it may lead to failure of another pregnancy. However, comprehensive screening involves a large number of tests, which is not only time-consuming but also expensive. Therefore, in clinical practice, the scope of screening can be appropriately narrowed and appropriate and necessary screening items can be selected based on the length of pregnancy and fetal status of the miscarriage. What are the causes of recurrent miscarriage? 1. Embryonic chromosomal abnormalities Embryonic chromosomal abnormalities are the most common cause of spontaneous miscarriage, but as the number of miscarriages increases, the possibility of embryonic chromosomal abnormalities gradually decreases. For couples with a history of recurrent miscarriage, karyotype analysis of peripheral blood lymphocytes should be performed to observe whether there are numerical and structural aberrations and types of aberrations to infer the probability of recurrence and implement genetic counseling. If possible, karyotyping of abortion products should be performed. There is no effective treatment for miscarriages caused by chromosomal abnormalities, and they need to be treated separately according to the type of chromosomal abnormality in both spouses. Carriers of Robertson homozygous translocation should be contraceptive or sterilized to avoid repeated miscarriages or delivery of abnormal children; carriers of autosomal balanced translocation and Robertson non-homozygous translocation need prenatal diagnosis to decide whether to terminate the pregnancy. 2. Uterine structural abnormalities Recurrent miscarriage due to uterine structural abnormalities account for 12%-15%, including congenital malformations of the uterus, uterine cavity adhesions, uterine fibroids, adenomyosis and cervical insufficiency and other diseases. Miscarriages due to anatomical factors are basically late miscarriages. Pelvic ultrasonography is currently recommended for all women with recurrent miscarriage to clarify the external morphology of the uterus, the thickness of the endometrium, and the presence of fibroids. Further definitive diagnosis through hysteroscopy and laparoscopy is needed for those suspected of having uterine abnormalities. For patients with recurrent miscarriage in the presence of saddle-shaped uterus, orthopedic uterine surgery is feasible. Septal uterus and uterine adhesions are mostly treated by hysteroscopic removal of the longitudinal septum or loosening of adhesions. For those with cervical insufficiency, prophylactic cervical cerclage can be performed as appropriate. Endocrine abnormalities Endocrine abnormalities are also a common cause of recurrent miscarriage. In addition to gynecological endocrine abnormalities, thyroid function abnormalities and diabetes mellitus may cause miscarriage. Female hormones are usually checked, including prolactin, folliculopoietin, luteinizing hormone, estrogen and androgen on the 3rd day of menstruation and progesterone on the 12th day after ovulation. Thyroid function (triiodothyronine, thyroxine, thyroid stimulating hormone) and blood glucose should also be tested, and a glucose tolerance test should be performed if necessary. It is generally recommended that patients with a history of recurrent miscarriage with hyperthyroidism should begin pregnancy after the condition is controlled; in mild cases, antithyroid medications such as propylthiouracil are used during pregnancy, and no congenital malformations associated with propylthiouracil have been identified. For those who have been diagnosed with hypothyroidism, it is recommended that pregnancy be considered after 3 months of normalization of thyroid function and that thyroid hormone must be taken consistently during pregnancy. 4. Pre-thrombotic state Pre-thrombotic state includes two types: congenital and acquired. The former is caused by mutations in genes related to coagulation and fibrinolysis, while the latter is caused by antiphospholipid antibody syndrome, acquired homocysteinemia, and various other diseases that cause blood thrombosis.