A double test is a test performed during pregnancy to examine possible chromosomal abnormalities in the fetus. Based on the results of the double test, the risk of chromosomal abnormalities such as Trisomy 21 (Down syndrome) and Trisomy 18 (Edwards syndrome) is assessed. The optimal time to perform a double test is between 11 and 14 weeks of pregnancy. When performing the test, an ultrasound scan is performed first. On the same day, the woman gives a blood test. It is important that the blood test is performed on the day of the ultrasound scan.