Abstract

A comparison of three different prenatal screening strategies for Down's syndrome found that contingent screening is the most cost effective. Contingent screening was unique in that it allowed the majority of expectant mothers to be reassured at the first trimester. Moreover, since contingent screening has the lowest cost per case of Down's syndrome detected and results in cost-savings, it may be a good screening strategy to implement nationally.

Background: Although there exist several options for prenatal screening for Down's syndrome, there is no consensus on the most cost-effective alternative. New screening strategies, such as the integrated test, sequential screening, and contingent screening, which combine analyses from first and second trimesters of pregnancy, allow for a relatively high detection rate. Published evaluations of new screening programs for Down's syndrome have primarily focused on detection rates; but the cost effectiveness ratio and similar end points of screening strategies are needed for the development of optimal public health strategies. This study assessed and compared the cost effectiveness of three strategies (i.e., the integrated test, sequential screening, and contingent screening) for prenatal screening for Down's syndrome.

Methods: Computer simulation was used to compare integrated, sequential, and contingent screening strategies. The simulation used the data from the Serum Urine and Ultrasound Screening Study with real unit costs for health care intervention, and a population of 110,948 pregnancies from Quebec in 2001. The main outcome measures were cost effectiveness ratios, incremental cost effectiveness ratios (ICERs), and other screening outcomes (e.g., the false positive rate, and the number of procedure-related miscarriages).

Findings: Contingent screening dominates all other options: it has the best cost effectiveness for achieving a lower overall false positive rate leading to better outcomes, fewer procedure-related miscarriages and unnecessary terminations, lowest cost per case of Down's syndrome detected, and the best ICER. When compared with screening based on maternal age alone, contingent screening costs $30,963 less per additional birth with Down's syndrome prevented. Contingent screening was also the only screening strategy that offered early reassurance to the majority of women in the first trimester and by limiting retesting during the second trimester was able to minimize costs.

Conclusions: Contingent screening is the preferred option for prenatal screening for Down's syndrome. Risk levels (or the probability of carrying a baby with Down's syndrome) are often misunderstood by patients, and it may be difficult to refuse a diagnostic test at first trimester for an anxious woman because some women want an early diagnosis. Policy makers should keep in mind that the use of a prenatal screening test which is not cost-effective or the use of inappropriate risk cut-off points (i.e., when to refuse a diagnostic test) in the first trimester may produce an excess in adverse complications and costs. More broadly, the results that contingent screening is cost-effective, results in cost-savings, and has the lowest cost per case of Down's syndrome detected, suggest that this screening strategy may be a good option to implement nationally.

References

Gekas J, Gagne G, Bujold E, Douillard D, Forest J, Reinharz D, Rousseau F. Comparison of different strategies in prenatal screening for Down's syndrome: cost effectiveness analysis of computer simulation. BMJ, 2009; 338: b318.