The combined sensitivity of age, nuchal translucency and maternal serum biochemistry for Down's syndrome was 84% (27/32). The relative risk for Down's syndrome was 0.17 (95% CI 0.07-0.41) for the women with normal scan findings at 18-23 weeks. The prevalence of isolated echogenic intracardiac foci at 18-23 weeks was 0.9% (144/16,917). None of these pregnancies were affected by Down's syndrome.