First of all, it is important to know that most of these tests are screening tests, not diagnostic tests. Screening tests are performed as a result of the detection of genetic structures belonging to the child and circulating freely in the mother's blood, which is the "Free Cell DNA" method, which is started to be performed at the earliest 9th week, and its accuracy rate is higher than other screening tests.
Other tests are 11-14 days of pregnancy. Double screening test performed with 2 biochemical parameters and evaluated together with ultrasound between weeks 15-20. It is a triple screening test performed with 3 biochemical parameters and evaluated together with ultrasound.