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Fetal Down syndrome screening: a cost effectiveness analysis of alternative screening programs |
Cusick W, Vintzileos A M |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The health interventions examined were screening programmes for Down syndrome (DS), based on advanced maternal age, second trimester triple screen (TS), and second trimester ultrasound (U/S) for foetal markers of DS. Five screening programmes were compared.
Programme 1: no screening in women aged younger than 35 years; amniocentesis (AM) in women aged at least 35 years.
Programme 2: TS for women younger than 35 years, followed by AM for those who were screen-positive; AM for women aged at least 35 years.
Programme 3: TS for all women, with AM for those who were screen-positive.
Programme 4: TS for women aged under 35 years, followed by U/S for screen-positive women and AM for those with foetal markers of DS on U/S; TS for women aged at least 35 years followed by AM for those who were screen-positive.
Programme 5: in all age classes, TS was followed by U/S for those who were screen-positive, which was followed by AM for those women with foetal sonographic markers for DS.
Economic study type Cost-effectiveness analysis.
Study population The study population comprised all women in delivery status in the state of Illinois (USA) in 1988.
Setting The setting was unclear, but it appears to have been that of the institutions that can conduct screening tests for DS. The study was carried out in Illinois, USA.
Dates to which data relate Both the effectiveness evidence and resource use data were derived from studies published between 1988 and 1998. The price year was 1996.
Source of effectiveness data The effectiveness evidence was derived from some published studies. In addition, the authors made assumptions about the effectiveness.
Outcomes assessed in the review The main health outcomes assessed from the literature were the sensitivity of each test and the screen-positive rate. The screen-positive rate was defined as "the number of women with normal foetuses who nevertheless are identified as being at increased risk for foetal Down syndrome". Another effectiveness estimate was the residual risk. This was calculated by dividing the number of undetected cases of DS by the total number of women not undergoing AM. The authors made assumptions to support the data obtained from the literature. All the health outcomes were calculated for the overall population of 167,654 women in delivery status, in the state of Illinois, in 1988.
Study designs and other criteria for inclusion in the review Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included Eight primary studies provided the effectiveness evidence. Delivery statistics in 1998, for the state of Illinois, were also used.
Methods of combining primary studies Investigation of differences between primary studies Results of the review The screen-positive rate was 8.4% for programme 1, 14.9% for programme 2, 8.3% for programme 3, 2.7% for programme 4, and 1.2% for programme 5.
The sensitivity was 30% for programme 1, 68.5% for programme 2, 62.3% for programme 3, 50.7% for programme 4, and 35.8% for programme 5.
The number of AM per case of DS was 181 for programme 1, 132 for programme 2, 77 for programme 3, 33 for programme 4, and 19 for programme 5.
The residual risk in women younger than 35 years was 0.12% for programme 1, 0.06% for programme 2, 0.06% for programme 3, 0.07% for programme 4, and 0.09% for programme 5.
The residual risk in women aged at least 35 years was 0% for programme 1 and programme 2, 0.14% for programme 3 and programme 4, and 0.25% for programme 5.
Methods used to derive estimates of effectiveness The authors made some assumptions about the effectiveness.
Estimates of effectiveness and key assumptions It was assumed that all pregnant women underwent foetal DS screening and that AM was performed in all women at high risk. In addition, a 1/250 procedural-related loss rate due to AM was assumed. Consequently, the number of pregnancy losses due to AM was 56 for programme 1, 100 for programme 2, 55 for programme 3, 17 for programme 4, and 7 for programme 5. In a population of 100,000 pregnancies, the losses due to AM were 34 for programme 1, 60 for programme 2, 33 for programme 3, 11 for programme 4, and 5 for programme 5.
Measure of benefits used in the economic analysis The benefit measure used in the economic analysis was the number of cases of DS detected. This was derived directly from the effectiveness analysis. The loss of non-DS foetuses due to AM was also accounted for.
Direct costs Discounting was irrelevant due to the short timeframe of the analysis. The only unit costs included in the analysis and reported in the paper were those for the maternal serum triple screen, the U/S examination and AM. The cost/resource boundary adopted was that of the reimbursement system. The costs and the quantities were estimated using the actual regional cost averages in 1996 for the state of Illinois. The source of the cost data was not reported. The dates during which the resource use data were gathered were not reported. The price year was 1996.
Statistical analysis of costs No statistical analysis of costs was conducted.
Indirect Costs The indirect costs were not included.
Sensitivity analysis Univariate sensitivity analyses were conducted to assess the effect of varying the sensitivity of U/S on the cost per DS case detected in programmes 4 and 5.
Estimated benefits used in the economic analysis Out of an estimated 260 cases of foetal DS, programme 1 detected 78 cases, programme 2 detected 178, programme 3 detected 162, programme 4 detected 132, and programme 5 detected 93.
The loss of non-DS foetuses due to AM was 56 for programme 1, 100 for programme 2, 55 for programme 3, 17 for programme 4, and 7 for programme 5.
Cost results The total cost of the screening interventions was $14,100,000 for programme 1, $36,100,000 for programme 2, $26,100,000 for programme 3, $20,000,000 for programme 4, and $18,000,000 for programme 5.
The total cost of the screening interventions in a population of 100,000 pregnancies was $8,400,000 for programme 1, $21,600,000 for programme 2, $15,600,000 for programme 3, $11,900,000 for programme 4, and $10,700,000 for programme 5.
Synthesis of costs and benefits The costs and the benefits were combined by calculating the average cost per case detected. This was $181,000 for programme 1, $203,000 for programme 2, $162,000 for programme 3, $151,000 for programme 4, and $194,000 for programme 5. Sensitivity analyses showed that, as expected, the cost per case for programmes 4 and 5 was affected by the sensitivity of U/S.
Authors' conclusions The authors concluded that "Down syndrome (DS) screening incorporating TS in all patients with programme 4 and without programme 3 selective U/S in women less than 35 years old yield the best combination of sensitivity and cost-effectiveness, while minimising the number of amniocentesis (AM)-related losses".
CRD COMMENTARY - Selection of comparators The rationale for the selection of the comparator was partially clear. The interventions were selected because they represented feasible options for screening programmes. In particular, programme 2 represented the standard approach for foetal DS screening in many regions in the USA. You should assess whether these are commonly used screening programmes in your own setting.
Validity of estimate of measure of effectiveness The effectiveness analysis used data derived from published studies, but a review of the literature was not performed. The effectiveness estimates derived from the literature were combined, but method used was not reported. As the authors noted, the screening sensitivity values used in the analysis were best estimates. This was because the fact that not all women can be expected to undergo screening, and not all women at risk for foetal DS decide to undergo AM, has to be taken into account. Finally, the authors made assumptions around some of the variables used in the analysis.
Validity of estimate of measure of benefit The benefit measure was derived directly from the effectiveness analysis. It would have been interesting had the authors assessed the patients' preferences for each screening programme, since not all women at risk for foetal DS may decide to undergo AM, due to the risk of procedural pregnancy loss and the eventual decision not to have elective termination for foetal DS. Also, the value of the life of the DS-affected person was not taken into consideration. Therefore, there is a bias in favour of detecting cases of DS. This could have been addressed, in part, by the use of life-years or quality-adjusted life-years, including those of the DS-affected person.
Validity of estimate of costs The unit costs of the screening tests were reported. The analysis of the costs included only the costs of the tests. The estimation of the costs appears to have been fairly specific for the study setting. The costs were treated deterministically and statistical analyses on the quantities were not conducted. The authors noted that it would have been interesting to have included the indirect costs or direct lifetime costs for children with DS, which appear to be of some importance in the case of the disease examined. Also, the definition of cost-effectiveness did not include the deleterious affect of AM. This could have been achieved by accounting for the benefit in terms of the life-years or quality-adjusted life-years.
Finally the analysis was not incremental. This health economist has found that programme 4 would have the lowest incremental cost-effectiveness ratio (incremental cost divided by the incremental effectiveness, compared with the next most effective strategy), followed by programme 3 and then 2. However, on this basis, programme 2 might still be chosen depending on the cost-effectiveness of other technologies to be funded from the same budget. As the authors point out, this must be weighted against the value of avoiding the loss of non-DS foetuses due to AM. On this basis, programme 5 is the best, followed by programmes 4, then 3 then 1. Programme 2 gives the most losses.
Other issues The authors did not make explicit comparisons of their findings with those from other studies. However, there were few bibliographic references with regards to the advantages of TS. The issue of the generalisability of the study results to other settings was not explicitly addressed, and sensitivity analyses were only conducted on the sensitivity of U/S. This could have limited the external validity of the analysis. However, the results were reported in full. The authors' conclusions might be found to be inappropriate for the population should the women's preferences be taken into consideration.
Implications of the study The authors highlight the crucial role of the physician in providing pertinent information to all pregnant women about the risks and benefits of the available screening tools for DS. This recommendation, however, should be contrasted with the following:
the failure of this study to take the women's preferences into account;
the failure to take the value of the life of DS-affected persons into consideration; and
the implicit higher value attributed to terminating DS foetuses than that attributed to preventing foetal losses.
Bibliographic details Cusick W, Vintzileos A M. Fetal Down syndrome screening: a cost effectiveness analysis of alternative screening programs. Journal of Maternal-Fetal Medicine 1999; 8(6): 243-248 Indexing Status Subject indexing assigned by NLM MeSH Adult; Amniocentesis /economics; Cost-Benefit Analysis; Down Syndrome /diagnosis /embryology /epidemiology; Female; Humans; Incidence; Mass Screening /economics; Maternal Age; Pregnancy; Pregnancy, High-Risk; Prenatal Diagnosis /economics; Risk Factors; Sensitivity and Specificity; Ultrasonography, Prenatal /economics; United States /epidemiology AccessionNumber 22000006099 Date bibliographic record published 31/08/2002 Date abstract record published 31/08/2002 |
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