There is no clinical term for how long a pregnancy is stable without miscarriage, because the fetus is not 100% stable before full-term delivery, especially in the first 3 months of pregnancy, the chance of miscarriage of the embryo is higher, while the fetus is relatively stable in the latter months, but there is still the possibility of miscarriage, of course, after 28 weeks it is not called miscarriage, but preterm delivery. A variety of factors may lead to miscarriage, such as embryonic factors, environmental factors, external stimuli, bad habits, maternal factors, etc.: 1. embryonic factors: if the embryo genetic abnormalities, in the process of fetal development, the fetal death may occur at any time, resulting in miscarriage; 2. environmental factors: if the pregnant woman is in an environment unfavorable to fetal development for a long time, such as chemical plants, laboratories or long-term exposure to toxic substances may cause miscarriage; 3, external stimuli: such as major surgery, too frequent sex, traumatic hemorrhage or direct impact on the abdomen, can lead to the occurrence of miscarriage. In addition, strong mental stimulation such as the death of relatives can also induce miscarriage; 4, bad habits: pregnant women who have alcoholism, excessive smoking, drug use and other behaviors during pregnancy may cause miscarriage; 5, maternal factors: if suffering from gestational hypertension disease, gestational hyperglycemia, uterine malformation, cancer, etc., or serious infection occurred during pregnancy women, due to poor health, the body can not afford pregnancy It can also trigger miscarriage. Therefore, in daily life, pregnant women should pay attention to avoid environments that may cause damage to the fetus, maintain a good routine and habits, and complete pregnancy checkups on time under the guidance of a doctor to keep an eye on the condition of the fetus. Pregnant women should maintain a stable mood and can relieve mental stress by communicating with family members and other means. If symptoms such as mild abdominal pain and vaginal bleeding occur during pregnancy, they should go to the hospital for examination and receive targeted treatment in a timely manner.