Prenatal reflex DNA screening for Down's syndrome: enhancing the screening performance of the initial first trimester test

Abstract

Objective

Estimate effect of adding biochemical markers (alphafetoprotein, inhibin-A, placental growth factor) and ultrasound markers (ductus venosus pulsatility index, nasal bone examination) to enhance the Combined test in prenatal reflex DNA screening for Down syndrome.

Methods

Published data were used to estimate screening performance (detection rates [DRs] and false-positive rates [FPRs]) of the Combined test with additional markers according to the proportion of women reflexed to DNA testing and gestational age of marker measurements.

Results

If 10% reflexed, the addition of the three biochemical markers to the Combined test increases the DR from 90.8% to 92.3% with a small FPR increase (0.025% to 0.027%) with markers measured at 11 completed weeks' gestation. With markers measured at 13 completed weeks' gestation the DR increases from 87.7% to 95.2% with no change in the FPR (0.027%). The further addition of the two ultrasound markers increases the DR to 96.8% and 97.5% at 11 and 13 weeks' respectively with a small FPR decrease (0.024% to 0.022%).

Conclusion

Adding markers to the Combined test can maintain or improve screening performance with a lower proportion of women reflexed. Our results can be used to determine the most cost-effective reflex DNA screening policy. This article is protected by copyright. All rights reserved.

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