Comparison of different strategies in prenatal screening for Down's syndrome: cost effectiveness analysis of computer simulation

Abstract

Objectives: To assess and compare the cost effectiveness of three different strategies for prenatal screening for Down's syndrome (integrated test, sequential screening, and contingent screenings) and to determine the most useful cut-off values for risk.

Design: Computer simulations to study integrated, sequential, and contingent screening strategies with various cut-offs leading to 19 potential screening algorithms.

Data sources: The computer simulation was populated with data from the Serum Urine and Ultrasound Screening Study (SURUSS), real unit costs for healthcare interventions, and a population of 110 948 pregnancies from the province of Québec for the year 2001.

Main outcome measures: Cost effectiveness ratios, incremental cost effectiveness ratios, and screening options' outcomes.

Results: The contingent screening strategy dominated all other screening options: it had the best cost effectiveness ratio ($C26,833 per case of Down's syndrome) with fewer procedure related euploid miscarriages and unnecessary terminations (respectively, 6 and 16 per 100,000 pregnancies). It also outperformed serum screening at the second trimester. In terms of the incremental cost effectiveness ratio, contingent screening was still dominant: compared with screening based on maternal age alone, the savings were $C30,963 per additional birth with Down's syndrome averted. Contingent screening was the only screening strategy that offered early reassurance to the majority of women (77.81%) in first trimester and minimised costs by limiting retesting during the second trimester (21.05%). For the contingent and sequential screening strategies, the choice of cut-off value for risk in the first trimester test significantly affected the cost effectiveness ratios (respectively, from $C26,833 to $C37,260 and from $C35,215 to $C45,314 per case of Down's syndrome), the number of procedure related euploid miscarriages (from 6 to 46 and from 6 to 45 per 100,000 pregnancies), and the number of unnecessary terminations (from 16 to 26 and from 16 to 25 per 100,000 pregnancies).

Conclusions: Contingent screening, with a first trimester cut-off value for high risk of 1 in 9, is the preferred option for prenatal screening of women for pregnancies affected by Down's syndrome.

Fig 1 Simplified version of the decision model for screening options (panel A) and diagnosis procedure (panel B) used in computer simulation of prenatal screening strategies for Down’s syndrome. Not shown, but included in the real model, is the possibility that miscarriage occurs before testing or after test results are known

Fig 2 Effects of different prenatal screening strategies for Down’s syndrome on (A) rate of false positive results, (B) number of procedure related euploid miscarriages, and (C) number of live births with Down’s syndrome (all values are per 100 000 pregnancies)

Fig 3 Effects of different prenatal screening strategies for Down’s syndrome on (A) number of unnecessary terminations, (B) proportion of pregnancies affected by Down’s syndrome screened by a first trimester test, and (C) proportion of continuing pregnancies that proceed to a second trimester test (all values are per 100 000 pregnancies)