Current French practices for prenatal diagnosis of trisomy 21: a population-based study in Paris, 1992-97

The results and limitations of current French practices for prenatal diagnosis (PND) of trisomy 21 were examined, using population-based data from the Paris Registry for 1992-97 (219 000 births). Of 670 cases of trisomy 21 reported, 71.0 per cent were terminations of pregnancy (TOP). The PND rate among mothers 38 years and older, all of whom were offered amniocentesis, was 89.9 per cent. Nearly all affected births in this age class followed maternal decisions, either to refuse amniocentesis or continue the affected pregnancy. In younger mothers, the overall French prenatal screening policy (three ultrasound examinations plus serum screening from January 1997) led to an overall PND rate of 67.3 per cent; it reached 78.8 per cent in 1997. Ultrasound accounted for 73.4 per cent of diagnosed cases. Increased detection by nuchal translucency measurement is clearly visible from 1996 onward. The birth prevalence, 8.7 per 10 000 births, diminished only slightly over the study period. The increase observed in the total number of cases in 1996 and 1997, concomitant with PND practice trends, may be due primarily to earlier TOP, which precedes miscarriages that would otherwise have occurred without being recorded. Future trends in prevalence among births must be observed carefully.