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

To evaluate the sequential combination of ultrasound screening for fetal aneuploidy at 11-14 weeks with maternal biochemistry at 12-14 and 15-18 weeks of gestation.

A prospective study including 1,656 women, with a singleton pregnancy booked before 13 weeks of gestation. Nuchal translucency (NT) thickness was measured by transabdominal ultrasound examination. alpha-Fetoprotein, free betahCG and hCG were measured by immunoradiometric (12-14 weeks) or immunometric (15-18 weeks) assays. Derived risks were then calculated. Cutoff risks were chosen first arbitrarily at 1/250 and then adjusted for a 5% false-positive rate.

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. One was at low risk with NT, and another was at low risk by maternal serum screening, but sequential combination of screenings led to a 100% detection rate with cutoffs of 1/240, 1/160 and 1/250 for NT, first- and second-trimester biochemistry, respectively (i.e. for a cutoff adjusted for a 5% false-positive rate).

This preliminary study suggests a benefit in combining maternal age-related risk together with NT and biochemical markers in the first or the second trimester. The algorithm combining these risks needs to be established in a wide population.