Correlation and overlapping between nuchal translucency and triple test among Down syndrome-affected pregnancies

OBJECTIVES: To examine the correlation and extent of overlapping between first-trimester nuchal translucency (NT) and second-trimester triple test (TT) results in Down syndrome (DS)-affected pregnancies. METHODS: Results of both tests were obtained in 28 cases with DS. Inter-test correlation was performed by comparing the likelihood ratios (LRs). Screen-positive rates (risk >1:380) were calculated for different age groups by adjusting age-dependent background risk and tests' LRs. Overlapping referred to ratio between screen-positive cases by both tests simultaneously and total screen-positive cases by either one or both tests. RESULTS: No correlation was found between the tests' LRs (Pearson correlation test, r = 0.0487). The overlapping between the tests was 25% and 38.5% among young patients of 20 and 35 years of age, respectively. The average overlapping among patients between 25 and 35 years of age was approximately 33%. Only 3 of the 28 DS cases demonstrated LRs <1 by both tests and moreover none exhibited LRs <0.2 by both tests. CONCLUSIONS: The degree of overlapping of one third, between NT and TT, confirms the assumption that both tests utilized together improves DS detection. Screen- negative result, by both tests simultaneously, may reassure low-risk population and aid to reduce the number of non-indicated invasive tests.