[How to improve the screening and diagnosis of fetal aneuploidy?]

In France, prenatal screening for fetal aneuploidies is legally regulated and is based on second-trimester maternal serum screening at 15-18 weeks. In 2000, 15% of all pregnant women in the Yvelines district of Greater Paris underwent amniocentesis, for a background risk of 11300. This high rate of invasive testing is unacceptable, given the risk of miscarriage and the financial cost. Between 2001 and 2003 we prospectively studied the acceptability and efficacy of screening for fetal aneuploidy in a large unselected population, using a risk calculation approach based on maternal age and serum markers, together with nuchal translucency at 11-14 weeks. A total of 14909 women with a mean age of 30.7 years [18-46] years were included. Pregnancy outcome was known in 93% of cases. The prevalence of trisomy 21 was 1/292 (51/14 909). Using a cut-off risk of 11250, the detection rate was 40/51 (78.4%). The combined risk was > or = 1/250 in 422 women (2.9%). Thus, one case of trisomy was diagnosed per 10.6 invasive tests. The detection rate would be 85% for a 5% false-positive rate. Eleven cases of trisomy were not diagnosed in the first trimester, and five of these were detected at 20-24 weeks by ultrasound examination. There were 50 miscarriages, five of which (1%) followed CVS or amniocentesis. These results confirm those published over the past 12 years by authors using the same methodology and quality controls. Although the French national screening policy has successfully contained a trend towards more invasive testing (which now reaches nearly 50% in some parts of Italy), our results suggests that second-trimester screening has become obsolete and should be replaced by first-trimester screening and diagnosis. This approach would require appropriate quality controls and should be implemented at the regional level.