[Evaluation of trisomy 21 risk by serial determination of chorionic gonadotrophin hormone and alpha-fetoprotein: results of a national pilot study].

Previous studies, as early as 1984, have demonstrated the efficiency of maternal serum markers to screen for Down syndrome. These markers were AFP, hCG, oestriol and beta-1-glycoprotein. A pilot study was initiated in France in 1990 to evaluate these markers. It lasted from May 1990 until April 1991. 22,410 pregnancies were monitored in total, and 19,407 for women between 30 and 37 years of age. The pregnancy outcome was known for 20,151 cases (86.6%). Sensitivity and predictive value of the test was calculated on 17,362 dosages which outcome was known. The sensitivity based on hCG only was 59.4% (38/64) for trisomy 21 and positive predictive value 1.65% (38/2,307). This test is a better marker than maternal age. In the pilot study it induced a 13.2% rate of amniocentesis. If the risk was calculated using both hCG and AFP results, the performances of the test were better. At equal rate of amniocentesis, the double test increases the sensitivity (+9.5% at risk 1/200, +7% at risk 1/250, +14.4% at risk (1/350). The strategy of double dosages decreases the number of amniocentesis for a given sensitivity rate. This decrease is more spectacular for high levels of sensitivity. This pilot study confirms already published results. Maternal serum markers are the best tools, combined with maternal age to evaluate the risk of trisomy 21.