[Combined use of nuchal translucency, gestational age and maternal age for evaluation of the risk of trisomy 21].

PURPOSE: Despite the definition of new screening policies for fetal trisomies, based on nuchal translucency thickness (NT) or maternal serum, the prevalence of trisomy 21 remains high. We propose a strategy based on a combination of maternal age, gestational age and NT, measured at the first trimester ultrasound examination, for the assessment of risk. METHODS: We present, in this paper, a characterisation of the physiological increase of fetal NT between the 10th and the 14th week of gestation, in a preliminary study of 266 echographic examinations. Next we propose a calculation of the simultaneous risk of trisomy 21 based on marginal risks for maternal age and increased NT values available in the literature. RESULTS AND CONCLUSION: We propose to define a high-risk group associated to the NT marker by using a cut-off risk of 1/250 for the simultaneous risk. This criteria may, as well, be expressed by a pathological threshold of NT varying with maternal age and gestational age. Without questioning that women aged of 38 years or older are a high-risk group, this approach should allow an improvement of the prenatal screening for trisomy 21.