The "Consecutive Combined Test"--using double test from week 8 + 0 and nuchal translucency scan, for first trimester screening for Down syndrome

Abstract

Objective: To test the performance of the "Consecutive Combined Test", applied on a high-risk population. The classic "Combined Test" (Double test (DT) and Nuchal Translucency (NT) measurement on the same day at app. week 12) gives detection rates (DR) for Down syndrome (DS) of 80-90% for false positive rates (FPR) of 5%. In affected pregnancies, however, the low PAPP-A level is more pronounced, the earlier in pregnancy. Thus, we hypothesized that the Double Test could be taken as early as from week 8 + 0, without compromising the excellent performance of the Combined Test. This "Consecutive Combined Test" allows for a centralised laboratory function.

Methods: Inclusion criteria were maternal age > 35 years (80%) or a family history (20%). Double test was taken at a median gestational age (GA) = 10 weeks. NT was measured at GA = 11 + 0 - 13 + 6. A combined risk estimate of > 1:400 at birth was used as cut-off.

Results: 881 had the full test. Screen positive = 34. CVS with aneuploidy = 11 (6 trisomy-21, 5 others). FPR = 3.2%. Positive Predictive Value (PPV) = 17.6% for T-21.

Conclusion: The "Consecutive Combined Test" applied on a high-risk population seems to be highly efficient with a remarkably high PPV.