Objectives: To evaluate the introduction to two health districts of an antenatal serum screening programme for Down's syndrome using the triple test-measurement of alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin concentrations in second trimester serum samples.
Methods: All women delivering at the main maternity units in both districts were eligible for the screening programme. A serum sample was taken between 15 and 22 weeks' gestation, confirmed by ultrasound scan. An estimated risk of 1 in 250 or greater was considered to be a screen positive result and further diagnostic tests were offered. As far as possible the outcome of all screened pregnancies was recorded, and babies with Down's syndrome born to women who declined serum screening were also identified.
Results: 6990 singleton pregnancies were screened over a two year period, representing an estimated uptake of 67% (6990/ 10,443). After a screen positive result 80% of women (168/211; 95% confidence interval 74.2 to 85.1%) opted for amniocentesis. The false positive rate was 2.9% (203/6979; 95% confidence interval 2.5 to 3.3%). The detection rate in the screened population was 73% (8/11). The estimated cost of identifying one Down's syndrome affected pregnancy was about 31,000 pounds.
Conclusions: Successful introduction of the triple test to health districts where there is no established serum screening programme for neural tube defects is possible. The programme seems to be acceptable to most of those screened. Uptake of the programme is sufficient to make it more effective than a policy for Down's syndrome screening dependent on age only.