How Effective Is First-Trimester Screening for Trisomy 21 Based on Ultrasound Only?

Objective: To evaluate the most common first-trimester ultrasound features of fetuses with trisomy 21 (T21) and to examine the screening performance for Down syndrome (DS) using only ultrasound-based protocols. To investigate whether maternal age (MA) has an impact on the efficacy of the ultrasound-based screening methods. Methods: In a prospective study, 6,265 patients were examined. Two ultrasound-based risk calculation protocols were applied: ‘NT' (based on nuchal translucency) and ‘NT+' (based on NT and secondary markers). Results: A total of 5,696 patients were enrolled for analysis; 84 subjects with T21 were identified. Combinations of abnormal ultrasound markers were observed in only 1.2% of euploid fetuses compared to 71.5% of fetuses with T21. Among 17.9% of DS cases with cardiac anomaly, 14.3% comprised atrioventricular septal defects. For a false-positive rate of 3%, the detection rates of T21 were 73.8 and 91.7% for the ‘NT' and ‘NT+' protocols, respectively. The efficacy of both methods was affected by MA. Conclusions: Most of the fetuses with DS demonstrate a combination of ultrasound markers of aneuploidy in the first trimester. The ‘NT+' protocol is efficient and provides comparable performance as a combined screening test. It is a valuable method, especially when the access to biochemical analysis is restricted.