Combined screening test for trisomy 21 - is it as efficient as we believe?

J Perinat Med. 2017 Feb 1;45(2):185-191. doi: 10.1515/jpm-2016-0031.


Objectives: To compare two first-trimester screening strategies: traditional combined screening and the one based on ultrasound markers only. We investigated the effect of maternal age (MA) on the screening performance of both of these strategies.

Methods: This was a prospective observational study based on a non-selected mixed-risk population of 11,653 women referred for first-trimester screening. The study population was divided in two groups: combined screening (CS) and ultrasound-based screening (US). Absolute risk was calculated to determine the influence of MA on screening performance.

Results: The CS arm comprised 5145 subjects including 51 cases of trisomy 21 (T21), and the US arm comprised 5733 subjects including 87 subjects with T21. Seven hundred and seventy-five subjects were excluded from the study. For a false positive rate (FPR) of 3%, the detection rate (DR) of T21 in CS arm was 78% vs. 90% in US arm. For 5% FPR, DR was 84% and 94% in CS and US arm, respectively. MA had an influence on DR positive rates in CS: both DR and FPR for T21 increased with advance in MA.

Conclusions: The US protocol showed higher DR of T21 compared to the CS one. It may be considered as a viable alternative to CS for T21 where access to biochemical testing is limited.

Publication types

  • Comparative Study
  • Observational Study

MeSH terms

  • Biomarkers / blood
  • Chorionic Gonadotropin, beta Subunit, Human / blood*
  • Down Syndrome / diagnostic imaging*
  • Female
  • Humans
  • Mass Screening / methods
  • Mass Screening / statistics & numerical data*
  • Pregnancy
  • Pregnancy Trimester, First
  • Pregnancy-Associated Plasma Protein-A / metabolism*
  • Prospective Studies
  • Ultrasonography, Prenatal*


  • Biomarkers
  • Chorionic Gonadotropin, beta Subunit, Human
  • Pregnancy-Associated Plasma Protein-A