The main purpose of non-invasive dna test for pregnant women is to check the risk of chromosomal disorders such as trisomy 21, trisomy 18 & trisomy 13 in the fetus. Peripheral blood can be drawn at 12 weeks of pregnancy – 22+6 weeks of pregnancy to test for free DNA in the plasma to check for the presence of genetic disorders in the fetus. It mainly checks for the risk of Down’s syndrome with trisomy 21, Edward’s syndrome with trisomy 18, and Patau’s syndrome with trisomy 13. The accuracy rate can be more than 95%. These three syndromes are the more common chromosomal aneuploidy disorders that cause severe mental retardation and varying degrees of congenital malformations. If the non-invasive dna detects a high risk, further amniocentesis is needed for prenatal diagnosis to minimize the birth of malformed babies.