Spontaneous abortion is the termination of pregnancy caused by natural factors (not artificial) at less than 28 weeks of gestation and a fetus weighing less than 1000g. If it occurs before 12 weeks of gestation (<12 weeks of gestation), it is called early miscarriage; while if it occurs at or after 12 weeks (12 weeks ≤ <28 weeks of gestation), it is called late miscarriage. The incidence of spontaneous miscarriage is about 15%, of which 80% are early miscarriages, and spontaneous miscarriages cause serious physical and psychological damage to women. Couples who have miscarried are hurt and want to know what caused this miscarriage, so what are the causes of spontaneous miscarriage? 1, embryonic factors. Chromosomal abnormalities are the most common cause of early miscarriage, accounting for about 50% to 60%. Chromosomal abnormalities include numerical abnormalities and structural abnormalities. The common number abnormalities are 13, 18, 21-trisomy, followed by X monosomy. Structural abnormalities, such as chromosome balance translocation, inversion, deletion and chimerism can also cause spontaneous abortion. 2. Maternal factors. (1) Maternal severe infection, high fever, severe anemia, chronic wasting disease, chronic liver and kidney disease or hypertensive systemic disease can lead to miscarriage. Maternal infection with Toxoplasma gondii, rubella virus, cytomegalovirus can infect the fetus leading to miscarriage. (2) Abnormalities of reproductive organs: uterine malformation, submucosal uterine fibroids, uterine adenomyoma, uterine adhesions, etc. can affect the development of embryonic implantation and lead to miscarriage. Cervical insufficiency can lead to premature rupture of fetal membranes and late spontaneous abortion. (3) Inflammation of reproductive organs: such as vaginitis, cervicitis, endometritis, pelvic inflammatory diseases, etc. (4) Endocrine abnormalities: maternal luteal insufficiency, hyperprolactinemia, polycystic ovary syndrome, hypothyroidism, poor blood sugar control, etc. also cause miscarriage. (5) strong stress: severe physical stimulation during pregnancy (such as surgery, direct impact on the abdomen, too frequent sexual intercourse) or mental trauma such as excessive tension, anxiety, fear, sadness and other adverse stimuli can also lead to miscarriage. (6) Bad habits: Pregnant women who smoke excessively, drink alcohol, drink coffee excessively, and take drugs such as heroin have been reported to cause miscarriage. (7) Abnormal immune function: such as antiphospholipid antibodies and anti-glycoprotein antibodies, which only manifest clinically as miscarriage, or even repeated miscarriage; a few miscarriages also occur in pregnant women with positive anti-nuclear antibodies and positive anti-thyroid antibodies. 3.Father factor. Father's chromosomal abnormality can also lead to miscarriage. 4.Environmental factors. Excessive exposure to radiation, lead, formaldehyde, stupid and other chemical substances can cause miscarriage. If you are preparing for pregnancy or have a history of spontaneous miscarriage and have any of the above causes, you should actively seek help from doctors at the hospital to remove the causes as soon as possible and successfully conceive a healthy baby.