Combined first trimester nuchal translucency and second trimester biochemical screening tests among normal pregnancies

A. Herman*, Z. Weinraub, E. Dreazen, S. Arieli, S. Rozansky, I. Bukovsky, R. Maymon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We prospectively examined whether first trimester nuchal translucency (NT) and second trimester triple test (TT) results are correlated, and determined overlapping and mutual screen-positive rates. Results of NT, TT, amniocentesis and pregnancy outcome were obtained in 508 normal pregnancies. Inter-test correlation was performed by comparing the likelihood ratios (LR). Overlapping of screen-positive cases, of NT and TT, was determined by comparing mutual risks for Down syndrome (DS) livebirth of ≤ 1: 380. Combined screen-positive rates were evaluated by using summation risk (NT and/or TT exhibiting a risk ≤ 1: 380) and calculated risk (new risk ≤ 1: 380, based on multiplication of LR(N)(T) and LR(T)(T). Screen-positive rates between NT and TT differed significantly and when either test showed an increased risk for DS, the probability of the other to predict the same was negligible (p < 0.001). Overall screen-positive rates, at a risk ≤ 1: 380, were 2% and 5.7% for NT and TT, respectively. Summation and calculated combining methods were associated with 7.5% and 2.0% screen-positive rates, respectively. Amniocentesis was performed on 20.7% of the cases, mostly screen-negative ones. Our results showed that, in normal pregnancies, NT and TT do not correlate and that their combined calculated risk in normal pregnancies is associated with a low screen-positive rate of 2.0%. Copyright (C) 2000 John Wiley and Sons, Ltd.

Original languageEnglish
Pages (from-to)781-784
Number of pages4
JournalPrenatal Diagnosis
Issue number10
StatePublished - 2000


  • Combined risk
  • Down syndrome
  • Nuchal translucency
  • Screen-positive rate
  • Triple test


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