1, genetic factors, if a child has been born with an affected child, then the incidence of this birth will be much higher. 2, pathogenic factors in the late stages of pregnancy, toxemia of pregnancy, prone to placental embolism as well as insufficient blood supply to the umbilical vessels, affecting the oxygen supply to the fetal brain tissue. Abnormal placenta or umbilical cord, resulting in low fetal blood oxygen or ischemia. Blood group incompatibility, such as Rh factor reaction produces excessive bilirubin and amine in the fetus, causing toxic damage. After 35 weeks of gestation, Down syndrome is more likely to occur in intrauterine fetuses with growth retardation. The mother suffers from surgery, infection, trauma or multiple pregnancies, etc. 3, postnatal factors, hyperbilirubinemia, such as neonatal hemolysis causing karyograms, brain tissue neural tissue mitochondrial oxidative phosphorylation of uncoupling occurs, the brain neural tissue energy production is insufficient and degenerative necrosis, resulting in pediatric Down syndrome. Neonatal shock due to blood loss, infection, etc. Craniocerebral injury and epileptic convulsions, which affect the blood and oxygen supply to brain tissue. Pulmonary atelectasis, pulmonary hyaline membrane disease, pulmonary edema, intrauterine pneumonia and gastric contents aspiration and other respiratory system diseases caused by cerebral hypoxia. 4, the mother’s age increases, the chance of children’s morbidity also increases. In other words, the chance of having a child with Down’s syndrome after the age of 40 is 100 times higher than that before the age of 25, regardless of the number of children. These data also tell us that prenatal diagnosis is necessary for older mothers, but it is not impossible for younger mothers to give birth to a child with Down’s syndrome. The average age of women giving birth to children with Down’s syndrome has decreased in recent years, both nationally and internationally, and may be related to factors such as teratogenic substances and infections. As for whether the age of men affects the incidence of children, there is no definite conclusion yet. 5. Teratogenic substances in the living environment such as radiation, benzene, pesticides, etc., and certain drugs such as sulfonamide can cause chromosomal aberrations. Women who have been exposed to radiation in the abdomen before pregnancy or early pregnancy, or have been exposed to other teratogenic substances several times, or have had viral infections, have a significantly higher chance of having Down’s syndrome in their children. Due to genetic factors, if a woman has had a child with Down syndrome, she has a higher than average chance of having a baby who is affected the second time.