Prospective experience with integrated prenatal screening and first trimester combined screening for trisomy 21 in a large Canadian urban center

Objectives To evaluate the performance of integrated prenatal screening (IPS) and first trimester combined screening (FTS) for trisomy 21 in a large Canadian urban center. Method Prospective data collection on women having FTS at one center from 1 November 2003 to 31 December 2005, or IPS at another from 1 January 2003 to 31 December 2005. A positive screen was defined as adjusted risk for trisomy 21 ≥ 1/200 at term or nuchal translucency ≥ 3.5 mm. Results 32 227 and 14 487 women were screened in the IPS and FTS programs, respectively. Detection rates (DRs) and positive rates (PRs) for trisomy 21 were 88.4% (95% CI: 81.6–91.5) and 3.3% (95% CI: 3.1–3.5) for IPS, and 83.9% (95% CI: 74.7–93.0) and 4.0% (95% CI: 3.7–4.3) for FTS. DR adjusted for viability bias was 85.2% for IPS and 78.6% for FTS. Applying both the screens to the 78 134 women who submitted prenatal screens in Ontario in 2005, thereby eliminating the effect of differences in the distribution of maternal age between screens, gave a DR (corrected for viability bias) and PR of 81 and 3.1% for IPS, and 76 and 3.4% for FTS. Conclusions Both IPS and FTS perform well and are feasible in a practical clinical setting. Copyright © 2008 John Wiley & Sons, Ltd.