[New methods of prenatal screening for trisomy 21]

Down syndrome is the most commonly recognized genetic cause of mental retardation. The risk of trisomy 21 is directly related to maternal age which can be viewed as the first screening test in the 1970's. New strategies for Down syndrom, have emerged with higher sensitivity and lower false-positive rate. These strategies are based on sonographic and maternal serum markers. The most specific but complex strategy is based on the integrated test, i.e., the integration of the quadruple test performed in the second trimester to the first trimester combined screening: for a 85% detection rate, the false positive rate is estimated to 0.9%. This strategy deprives the patient of an early diagnosis. Alternatives strategies do exist which can perform similar detection rate but with increasing false positive rate. To date Down syndrom, screening has not been coordinated by a national body; it would be usefull to ensure the sonographist formation, perform quality audit and decrease variations in practice.