I. What is Down syndrome? Down syndrome is the most common type of chromosomal abnormality, also known as trisomy 21, with a prevalence of about one in 800 (1/800) live births in the population. Children with Down syndrome have an extra chromosome 21, and most will have growth defects, mental retardation, congenital heart disease, passive palms, and a number of peculiar facial features, as shown below. The typical life expectancy of a Down’s child is about 40 years. The risk of a pregnant woman carrying a Down’s child increases significantly with the age of the mother. In order to detect high-risk pregnant women in time for prenatal diagnosis, pregnant mothers can undergo Down’s screening. What is Down’s syndrome screening? Down’s syndrome screening generally involves taking 2 milliliters of blood from the pregnant mother, testing the serum concentrations of alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), and free estriol (uE3), and then combining them with the mother’s expected date of delivery, age, weight, and gestational age at the time of the blood collection, to calculate a risk coefficient of a Down’s syndrome baby. The risk factor of “Down’s syndrome” will be calculated. Why must do Down’s syndrome Down’s syndrome can cause fetal malformations in physical development, delayed development of motor, language and other abilities, serious intellectual disabilities, most of which are accompanied by a variety of complex diseases, such as heart disease, infectious diseases, amblyopia, hard of hearing, etc., and can not take care of their own lives. This is why it is important to understand the significance of prenatal screening before it is done, so that the anxiety associated with the results can be reduced and the patient understands that a low-risk screening test can result in the delivery of a sick fetus. Prenatal screening is not just about checking blood markers, but also with the help of a series of factors (e.g., week of gestation, weight, age, smoking, type I diabetes, and other factors), which ultimately leads to the chances of fetal abnormalities in a pregnant woman. These results are not a diagnosis of whether the fetus is sick or not, if the results are high risk, it just means that the fetus has a high risk of disease and needs further prenatal diagnosis. Fourth, the best time for testing is 15 to 20 weeks of pregnancy. Pregnant mothers who are 35 years old ( meaning 35 years old at the time of delivery) or older and other pregnant mothers with a history of abnormal deliveries should consult with their obstetrician about prenatal diagnosis such as amniocentesis (amniocentesis is amniocentesis screening, which is the most commonly used invasive prenatal diagnostic technique). A screening result of “low risk” indicates a low risk and “high risk” indicates a high risk. Even if the result is high risk, the mother should not be alarmed, because it is not always possible to have a child with Down’s syndrome in the high-risk group, and amniotic fluid karyotyping is needed to confirm the diagnosis. The percentage of “high risk” Down’s test results is not high, so mothers should not worry too much.