The etiology of miscarriage is very complex and has been a hot topic of research in the past 20 years. It is generally believed that for early spontaneous abortion occurring before 12 weeks of pregnancy, the common causes are chromosomal abnormalities, luteal insufficiency, immune factors and infections, while for late spontaneous abortion occurring between 12 and 28 weeks of pregnancy, the common causes are uterine malformation, relaxation of the endocervix and systemic diseases. Once there is a history of multiple miscarriages, a series of relevant examinations should be carried out to rule out the relevant diseases or after the relevant diseases have been treated and cured before pregnancy. Genetic factors: Embryonic dysplasia due to abnormal number or structure of chromosomes is a common cause of recurrent spontaneous miscarriage. In early pregnancy spontaneous abortion, the incidence of karyotypic abnormalities is as high as 60% to 70% (aborted children with chromosomal abnormalities account for 50% to 60%, and one or both spouses with chromosomal abnormalities account for about 10%). This shows that genetic factors are the most important culprits of spontaneous abortion, especially in the first trimester of pregnancy. Since the report of chromosomal abnormalities associated with recurrent spontaneous abortions in couples in 1962, chromosomal abnormalities in miscarrying couples have attracted widespread medical attention and have been studied extensively. Chromosomal testing of both couples and miscarriage products has also been included as a routine test. The common karyotypic abnormalities found in the chromosome examination of couples are: translocations (44%), chimerism (48%), deletions or inversions (8%). Carriers of autosomal balanced translocations and non-homozygous Loboson translocations have a theoretical chance of delivering a normal karyotype and carrier baby, and prenatal testing should be done for these couples to ensure a normal baby. Couples who are not medically advised to have children should not be forced to do so. Another situation is when both couples are chromosomally normal, but chromosomal abnormalities occur during gamete formation and embryo development. For example, if a woman is older than 35 years old and her eggs are aging, she is prone to chromosomal non-separation, resulting in chromosomal abnormalities. Endocrine factors: 20%-25% of recurrent spontaneous miscarriages are caused by endocrine abnormalities, of which early miscarriages are commonly caused by luteal insufficiency. 1, luteal insufficiency: the ovarian corpus luteum secretes progesterone, and insufficient progesterone will lead to endometrial dysplasia, preventing implantation of the pregnant egg and early embryonic development. Before 8 weeks of gestation, the main source of progesterone is the corpus luteum of pregnancy. After 8 weeks of gestation, the placental trophoblast gradually replaces the corpus luteum as the main source of progesterone. If progesterone is insufficient before 8 weeks of gestation, it will lead to miscarriage. 2, hyperprolactinemia: lactogen inhibits the function of the corpus luteum, making the luteal phase shorter and progesterone insufficient, at the same time, it can also affect the local normal level of lactogen in the uterus, affecting the development of the embryo and causing miscarriage. 3, endometriosis: endometriosis patients have a high rate of spontaneous miscarriage, about 30%. The causes and mechanisms of miscarriage are complex. Comprehensive treatment is needed. 4. Polycystic ovary syndrome: About 40% of patients with polycystic ovary syndrome have recurrent spontaneous abortions, mainly due to concomitant hyperprolactinemia, luteinizing insufficiency, low estrogen levels, poor egg quality and endometrial abnormalities. The disease can be treated and should be reproduced without problems. 5. Thyroid dysfunction and diabetes mellitus: this type of disease can also lead to habitual miscarriage. Anatomical factors: mainly include congenital uterine development abnormalities, such as infantile uterus, unicornuate uterus, bicornuate uterus, longitudinal/transverse uterine septum, uterine cavity adhesions, submucosal fibroids, polyps, cervical insufficiency, etc. Miscarriage can occur in early pregnancy (insufficient blood flow to the embryonic site) or in mid-pregnancy (structural defects of the uterus, abnormal tolerability, insufficient blood supply). For most anatomical causes of recurrent spontaneous abortion, targeted surgery can be performed. Especially for those with simple cervical insufficiency, the timely choice of endocervical cerclage is very effective. Fourth, the infection factor: female reproductive tract infection of a variety of pathogens can lead to miscarriage, common are mycoplasma, chlamydia, toxoplasma, gonococcus, listeria, herpes simplex virus, rubella virus, cytomegalovirus and protozoa. Screening for these pathogens is basically included in the routine TORCH five tests. Most of these infections, which have no obvious symptoms, should be examined before pregnancy to prevent accidents. V. Immune factors: In addition to chromosomal abnormalities, endocrine disorders, structural malformations of the reproductive system and infections, the cause is unknown in about 60% – 70% of patients. In recent studies, it is believed that about 30% of the patients with unknown causes are related to autoantibody production, which may be autoimmune disease, called autoimmune recurrent spontaneous abortion during normal pregnancy, the embryo has 1/2 genetic material of the father’s homozygous natural transplants, in order to ensure that the embryo is not rejected by the mother, the maternal immune function undergoes many changes, including the formation of specific immunosuppressive substances (such as confinement antibodies, inhibitors). The immune system is composed mainly of specific immunosuppressive substances (e.g., closed antibodies, suppressive T cells, etc.) and non-specific suppressive factors. All immune factors are organically coordinated to maintain pregnancy. After pregnancy, the mother rejects the fetus and miscarriage occurs due to immune maladjustment between mother and child. Recurrent spontaneous abortion occurs when there is an abnormality in one of the immune factors. Commonly detectable immune abnormalities include maternal closed antibody deficiency, certain autoantibodies in the serum, such as anticardiolipin antibodies, anticore antibodies, and antithyroid antibodies. Blood group incompatibility, positive anti-sperm antibodies, etc. Late miscarriage is often caused by maternal and child blood group incompatibility, such as ABO and Rh blood group incompatibility. Systemic diseases: Serious systemic diseases, such as cardiovascular diseases, kidney diseases, blood diseases, acute infectious diseases, certain sexually transmitted diseases and autoimmune diseases can lead to miscarriage. Environmental factors: Toxic substances that can lead to miscarriage include cadmium, lead, organic mercury, DDT and other radioactive substances, high temperature, etc. These harmful factors lead to miscarriage due to lethal mutation or damage to the genetic material of the embryo. Alcoholism, female smoking, etc. can also cause miscarriage. Eight, male factors: this factor is often ignored in the past, in fact, semen factors, semen is not liquefied, high sperm malformation rate, low sperm vitality, sperm agglutination and other male factors can cause miscarriage. It is clinically observed that its paternal bacteriophage spermia, which accounts for about 10-15%. Asymptomatic infected semen in the male reproductive tract, i.e. containing a certain number of bacteria, viruses, Chlamydia trachomatis, Mycoplasma urealyticum, etc., these infections can weaken the ability of the pregnant woman to conceive and cause the embryo to abort. Bacteria can also be carried by active sperm during the “kiss of life”, which can interfere with sperm-egg union and implantation. Most of the bacteria carried are Streptococcus faecalis, Staphylococcus albus, Escherichia coli, anaerobic bacteria, etc. Abnormal semen, such as oligospermia and polyspermia ERSA prevalence is 37.6% and 20%, respectively. Increased malformed sperm can also cause ERSA,dead malformed sperm are not likely to be fertilized and thus not associated with ERSA, so attention should be paid to the morphology of live sperm when examining sperm morphology. Most sperm with macrocephaly are diploid and form polyploid embryos after fertilization resulting in miscarriage. This aspect should be examined once this type of disease occurs.