Efficiency of ultrasound and biochemical markers for Down's syndrome risk screening - A prospective study

Objective: To evaluate the sequential combination of ultrasound screening f or fetal aneuploidy at 11-14 weeks with maternal biochemistry at 12-14 and 15-18 weeks of gestation. Methods: A prospective study including 1,656 wome n, with a singleton pregnancy booked before 13 weeks of gestation. Nuchal t ranslucency (NT) thickness was measured by transabdominal ultrasound examin ation. a-fetoprotein, free beta hCG and hCG were measured by immunoradiomet ric (12-14 weeks) or immunometric (15-18 weeks) assays. Derived risks were then calculated. Cutoff risks were chosen first arbitrarily at 1/250 and th en adjusted for a 5% false-positive rate. Results: Seven fetal aneuploidies were diagnosed, including 5 Down's syndromes, 1 trisomy 18 and 1 triploidy . Three Down's syndromes had concordant high risk with the 3 screenings. On e was at low risk with NT, and another was at low risk by maternal serum sc reening, but sequential combination of screenings led to a 100% detection r ate with cutoffs of 1/240, 1/160 and 1/250 for NT, first- and second-trimes ter biochemistry, respectively (i.e. for a cutoff adjusted for a 5% false-p ositive rate). Conclusion: This preliminary study suggests a benefit in com bining maternal age-related risk together with NT and biochemical markers i n the first or the second trimester. The algorithm combining these risks ne eds to be established in a wide population.