Down’s syndrome screening is more accurate when done between 12-16 weeks of pregnancy, when the fetus is also the right size. During the screening, a comprehensive analysis of the maternal serum is done to assess the development of the fetus and determine if there are any congenital genetic problems based on the age, gestational age and weight of the mother. Down’s syndrome screening can detect the presence of trisomy 21 and trisomy 18, and the accuracy rate of Down’s syndrome screening can reach 65%. If the screening is moderate or high risk, further tests are needed, such as non-invasive DNA or amniotic fluid extraction, to accurately determine whether the baby has congenital genetic problems.