The birth of a Down’s child is usually the result of trisomy 21 on chromosome 21, and is mostly unrelated to the presence or absence of chromosomal abnormalities in the parents. Down’s syndrome is also known as trisomy 21, which is caused by an abnormality of chromosome 21. Most cases of trisomy 21 are due to the fact that during the division of a fertilized egg, the sperm cell or egg cell divides abnormally, and chromosome 21 fails to divide, resulting in the creation of an extra chromosome 21, and the affected person has three chromosome 21’s in his or her body. Predisposing factors for the birth of a Down’s syndrome child include the mother being of advanced maternal age, the older the pregnant woman, the greater the chance of giving birth to a Down’s syndrome child; there are substances in the environment that cause malformations, such as reflexes, pesticides, medications, and other substances. If the mother is exposed to radioactive substances or viral infections before pregnancy or in the early stages of pregnancy, the chances of having a Down’s child are higher. Pregnant women who are at high risk of having a Down’s syndrome baby should consult a prenatal clinic in a timely manner and complete prenatal testing and diagnosis under the guidance of a doctor to reduce the chances of a Down’s syndrome baby being born.