At our center, we offer the ‘double screen’ which is a specialized blood test that checks for fetal hormones in the maternal blood. This is done starting at 10 weeks, or at the time of the first trimester scan (11w6d-13w6d). The levels of these hormones can be calculated with respect to the size of the baby and if abnormally high or low, they may alert us to abnormalities. This test is carried out on a machine that has been certified by the Fetal Medicine Foundation (a world authority on the first trimester testing) that fulfills their strict criteria as to safety and acceptable levels of error. When done in the first trimester of pregnancy and combined with the ultrasound that checks for all the markers of Down's Syndrome (trisomy 21), it has the ability to detect up to 96% of affected babies at an early point in the pregnancy. It has a better detection rate than the traditional "triple screen".