Down syndrome, also known as trisomy 21, may be associated with age-related, genetic, and environmental factors. Humans normally have 23 pairs (46) of chromosomes, and the normal chromosome karyotype is 46, XY. When the fertilized egg divides to form a human individual, if chromosome 21 is abnormal and does not segregate, an extra chromosome 21 will be present in the embryo’s somatic cells, which will lead to the development of the disease. 1. Age factor: the older the mother’s gestational age, the higher the risk of the disease, the mother’s age >35 years old is a high-risk factor, 40 years of age or older pregnant women to do amniocentesis screening, the detection rate of the disease is about 5% or more. 2 genetic factors: a small number of female patients with fertility, their offspring incidence rate of 50%, the parents of children with Down syndrome have a higher probability of giving birth to another child with the disease. 3. Environmental factors: early pregnancy exposure to teratogenic substances (such as radiation, pesticides, benzene, etc.), certain drugs such as sulfonamides can cause chromosomal aberrations. Chromosomal abnormalities can also be caused by exposure to radiation before or during early pregnancy (e.g. abdominal) and viral infections (e.g. Hepatitis B virus infection). If you have any other questions, it is recommended that you consult a medical professional for guidance.