Methods of prediction and prevention of pre-eclampsia: systematic reviews of accuracy and effectiveness literature with economic modelling

Abstract

OBJECTIVES: To investigate the accuracy of predictive tests for pre-eclampsia and the effectiveness of preventative interventions for pre-eclampsia. Also to assess the cost-effectiveness of strategies (test-intervention combinations) to predict and prevent pre-eclampsia. DATA SOURCES: Major electronic databases were searched to January 2005 at least. REVIEW METHODS: Systematic reviews were carried out for test accuracy and effectiveness. Quality assessment was carried out using standard tools. For test accuracy, meta-analyses used a bivariate approach. Effectiveness reviews were conducted under the auspices of the Cochrane Pregnancy and Childbirth Group and used standard Cochrane review methods. The economic evaluation was from an NHS perspective and used a decision tree model. RESULTS: For the 27 tests reviewed, the quality of included studies was generally poor. Some tests appeared to have high specificity, but at the expense of compromised sensitivity. Tests that reached specificities above 90% were body mass index greater than 34, alpha-foetoprotein and uterine artery Doppler (bilateral notching). The only Doppler test with a sensitivity of over 60% was resistance index and combinations of indices. A few tests not commonly found in routine practice, such as kallikreinuria and SDS-PAGE proteinuria, seemed to offer the promise of high sensitivity, without compromising specificity, but these would require further investigation. For the 16 effectiveness reviews, the quality of included studies was variable. The largest review was of antiplatelet agents, primarily low-dose aspirin, and included 51 trials (36,500 women). This was the only review where the intervention was shown to prevent both pre-eclampsia and its consequences for the baby. Calcium supplementation also reduced the risk of pre-eclampsia, but with some uncertainty about the impact on outcomes for the baby. The only other intervention associated with a reduction in RR of pre-eclampsia was rest at home, with or without a nutritional supplement, for women with normal blood pressure. However, this review included just two small trials and its results should be interpreted with caution. The cost of most of the tests was modest, ranging from 5 pounds for blood tests such as serum uric acid to approximately 20 pounds for Doppler tests. Similarly, the cost of most interventions was also modest. In contrast, the best estimate of additional average cost associated with an average case of pre-eclampsia was high at approximately 9000 pounds. The results of the modelling revealed that prior testing with the test accuracy sensitivities and specificities identified appeared to offer little as a way of improving cost-effectiveness. Based on the evidence reviewed, none of the tests appeared sufficiently accurate to be clinically useful and the results of the model favoured no-test/treat-all strategies. Rest at home without any initial testing appeared to be the most cost-effective 'test-treatment' combination. Calcium supplementation to all women, without any initial testing, appeared to be the second most cost-effective. The economic model provided little support that any form of Doppler test has sufficiently high sensitivity and specificity to be cost-effective for the early identification of pre-eclampsia. It also suggested that the pattern of cost-effectiveness was no different in high-risk mothers than the low-risk mothers considered in the base case. CONCLUSIONS: The tests evaluated are not sufficiently accurate, in our opinion, to suggest their routine use in clinical practice. Calcium and antiplatelet agents, primarily low-dose aspirin, were the interventions shown to prevent pre-eclampsia. The most cost-effective approach to reducing pre-eclampsia is likely to be the provision of an effective, affordable and safe intervention applied to all mothers without prior testing to assess levels of risk. It is probably premature to suggest the implementation of a treat-all intervention strategy at present, however the feasibility and acceptability of this to women could be explored. Rigorous evaluation is needed of tests with modest cost whose initial assessments suggest that they may have high levels of both sensitivity and specificity. Similarly, there is a need for high-quality, adequately powered randomised controlled trials to investigate whether interventions such as advice to rest are indeed effective in reducing pre-eclampsia. In future, an economic model should be developed that considers not just pre-eclampsia, but other related outcomes, particularly those relevant to the infant such as perinatal death, preterm birth and small for gestational age. Such a modelling project should make provision for primary data collection on the safety of interventions and their associated costs.