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Title: Economic issues in the provision of antenatal screening for Down's syndrome
Author: Deverill, Mark
ISNI:       0000 0001 3422 9426
Awarding Body: Newcastle University
Current Institution: University of Newcastle upon Tyne
Date of Award: 2008
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This thesis exammes the economiC issues related to the prOVISIon of antenatal screening for the genetic disorder commonly referred as Down's syndrome (DS). DS is associated with a number of serious medical consequences and an increased mortality rate. The offer of screening for DS to pregnant women has been a feature of antenatal care for over 30 years. In recent years an increasing number of screening techniques have been developed based on biochemical testing and ultrasound scanning. This thesis pays particular attention to three of these tests, nuchal translucency screening (NT), the combined test (CT), and the integrated test (IT). These three tests differ in terms of their efficacy in detecting cases of DS and differ by the time point (trimester) in the pregnancy that they can provide results to women. The empirical studies presented here examine issues of cost-effectiveness (for NT) and women's preferences (based on the characteristics of NT, CT, and IT) using the methods of standard gamble, a discrete choice experiment (DCE), and contingent valuation (based on willingness to pay). A conceptual model (Figure 2.1) is provided to underpin the empirical research that resulted from the review of key methodological issues discussed and presented in Chapter2. The cost-effectiveness analysis showed that once the issue of the spontaneous abortion of fetuses with DS has been accounted for, NT screening carried out in the first trimester of pregnancy may not detect significantly more cases of DS than a second trimester screening test based on biochemical testing alone. However, NT by definition does provide the screening result earlier in the pregnancy; but using NT does bring about a net increase in screening costs and produces a positive incremental costeffectiveness ratio. It should be noted that cost estimates produced here do not attempt to take into account any cost savings that may accrue to the health care sector or to other sectors as result of preventing the live birth of a child with DS. Probabilistic sensitivity analysis (with results taking into account spontaneous abortion of DS fetuses) showed that at a societal willingness to pay of £30 000 per DS case prevented there was only a 46% probability ofNT screening being cost-effective. The cost-effectiveness analysis of NT screening was complemented by a standard gamble survey in which women were asked to value DS screening scenarios based on various screening outcomes. The aim was to see if women placed more value on screening results presented earlier in the pregnancy (i.e. in the first trimester of pregnancy as opposed to the second trimester). The results found that women did not value earlier screening results more highly than later ones. This result held both for scenarios that featured negative screening results, i.e. a result showing that a pregnancy was not affected by DS, or positive screening results i.e. a result showing that a pregnancy was affected by DS followed by a termination of pregnancy. In very recent times in the UK the use of the CT or the IT has been strongly championed by various advocates. In essence they differ in that the CT offers first trimester results and the IT offers second trimester results. Empirical evidence also suggests they differ by efficacy in terms of the DS detection rates they achieve and by the number of false-positive screening results that occur. To gain more understanding of women's preferences with regard to the different attributes of these screening tests a DCE was undertaken. The results of this showed that women were more likely to choose a screening option that had high detection and low false-positive rates, that women preferred (when necessary) that the termination of an affected pregnancy was done using a medical termination, but that the timing of the test (as defined by week of pregnancy) was not statistically significant in the regression model. The sample of women that completed the DCE was given full descriptions of the CT and the IT and was asked to state a straight preference of one of the tests over the other. In addition they were also asked to state their maximum willingness to pay in order to guarantee their choice of screening test. The binary choice question (of CT or IT) showed an almost exact salsa split in choosing the CT or the IT. This result is not consistent with the findings described above that suggested that the timing of the test was not important but that test performance was important. In the description given to women the IT was shown to have a better detection rate than the CT and was no worse in terms of false-positive results. If women's preferences were driven by test performance and not by timing then the logical choice would be the IT. The empirical results presented shed new light on the key trade-offs that are involved when choosing amongst screening methods and it was demonstrated that the results from the various evaluative approaches used here do not always lead to the same conclusions. What the results did show is that the sole provision of anyone screening programme would not necessarily match the choices that women would make and that different groups of women (for example by age) may make different screening choices. This conclusion challenges the recently issued NICE clinical guidance on antenatal care that instructs providers of screening for DS in England and Wales to routinely use the CT in the first trimester of pregnancy. This highlights the gap between aspirations to use a wider evaluative approach by ascertaining and acting on the preferences of individual pregnant women and the imperative to use health care resources efficiently.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available