Combined screening test for trisomy 21 - is it as efficient as we believe?

Area of Science:

• Prenatal diagnostics
• Maternal-fetal medicine
• Genetics

Background:

• First-trimester screening is crucial for detecting fetal aneuploidies.
• Traditional combined screening (CS) involves maternal age, ultrasound markers, and biochemical tests.
• Maternal age (MA) is a known factor influencing screening performance.

Purpose of the Study:

• To compare the screening performance of ultrasound-only (US) versus combined screening (CS) for trisomy 21 (T21).
• To evaluate the impact of maternal age on the detection rates (DR) and false positive rates (FPR) of both strategies.

Main Methods:

• Prospective observational study of 11,653 women undergoing first-trimester screening.
• Population divided into CS (n=5145) and US (n=5733) groups.
• Absolute risk calculation to assess MA influence on screening performance.

Main Results:

• Ultrasound-only screening demonstrated higher T21 detection rates: 90% at 3% FPR and 94% at 5% FPR, versus 78% and 84% for combined screening, respectively.
• Maternal age significantly influenced combined screening performance, with increased DR and FPR for T21 in older women.
• The US protocol showed superior performance in T21 detection.

Conclusions:

• Ultrasound-only screening is a more effective method for detecting trisomy 21 compared to combined screening.
• The US protocol is a practical alternative for T21 screening, particularly in settings with limited access to biochemical testing.