Every mother is afraid that she will have a child with Down’s syndrome when she is preparing for pregnancy. One of the causes of Down’s syndrome: genetics 10% of Down’s syndrome is due to extra chromosomes from the father. Pregnant women who have had a child with Down syndrome once have a higher chance of having a second child with the disease than the general population. The second cause of Down syndrome is teratogenic substances and diseases. Teratogenic substances in the environment such as radiation, benzene, pesticides, and certain drugs such as sulfonamide can cause chromosomal aberrations. Women who have been exposed to radiation in the abdomen before pregnancy or in the early stages of pregnancy, or who have been exposed to other teratogenic substances, or who have had viral infections, have a significantly higher chance of having a child with Down’s syndrome. The age of the mother and father at the time of pregnancy is a major factor in the incidence of Down syndrome. As the age of the mother increases, the chance of having a child with Down syndrome increases. The incidence of Down’s syndrome is 1 in 2,000 for mothers under 25 years of age, 1 in 50 for mothers 35 to 39 years of age, and 1 in 20 for mothers over 40 years of age, which means that the chance of having a baby with Down’s syndrome after the age of 40 is 100 times higher than before the age of 25, regardless of the number of births. 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. In recent years, it has been found, both nationally and internationally, that the average age of women giving birth to children with the condition has decreased, which may be related to factors such as teratogenic substances and infections. As for whether the age of the male affects the incidence of the child, the jury is still out.