First trimester contingent test as a screening method for Down's syndrome. A prospective study in the general...

Area of Science:

• Prenatal screening
• Maternal-fetal medicine
• Genetics

Background:

• First-trimester screening for Down's syndrome (DS) is crucial for early intervention.
• Contingent screening strategies aim to optimize detection rates and minimize false positives.

Purpose of the Study:

• To assess the feasibility of a contingent test for Down's syndrome (DS) screening in the first trimester.
• To evaluate the sensitivity (Sen) and false positive rate (FPR) of this contingent approach.

Main Methods:

• A prospective study over 4 years involved pregnant women undergoing a combined test (CT) as the initial step.
• An intermediate risk group identified via CT was offered secondary ultrasound assessment of specific markers.
• Ultrasound markers included nasal bone, ductus venosus, and tricuspid regurgitation.

Main Results:

• The combined test (CT) achieved a sensitivity of 83% and a false positive rate (FPR) of 3%.
• The contingent test demonstrated a sensitivity of 70.8% and an FPR of 2%.
• In the intermediate risk group (1,036 women), 98.1% received secondary ultrasound assessments.

Conclusions:

• The contingent test successfully reduced the false positive rate (FPR) compared to the combined test.
• However, the sensitivity of the contingent test was too low for its implementation as a primary screening method for Down's syndrome (DS).