Methods
The economic evaluation took the perspective of the health system and its patients and compared the direct costs of the additional resources used from randomisation until the time of postnatal hospital discharge of the woman or her baby, whichever occurred last, with the increments in health outcome for both the woman and the baby in a cost-consequences analysis [
4,
5]. Women with a twin pregnancy were excluded from this economic evaluation because it was anticipated that their likely increased use of resources could not be robustly estimated due to their expected small numbers in the trial. This analysis included all costs, but only those primary clinical outcomes (consequences) that achieved a P-value less than 0.05 in the main trial after adjustment for the confounders of maternal age, race or ethnic group, and parity. The economic evaluation was designed to take the form of a cost-consequences analysis, since trading-off between the utilities (preference values) of mother and infant would entail difficult conceptual and ethical issues. The intention was to provide relevant information about the incremental value of the intervention to assist decision-makers in setting priorities for health resource allocation.
The costing reported in this paper began at the moment of randomisation, and ended at the initial postnatal hospital discharge of the woman or her baby, whichever occurred last. Direct costs were measured to the health system and charges to the woman and her family. Cost was calculated as the number of occasions of each service multiplied by its unit cost. More than 98% of participants were public hospital patients.
Obstetric hospital outpatient occasions of service after enrolment were collected from the trial data for all women with a singleton pregnancy. Unit costs were obtained from sources congruent with the Manual of Resource Items for use in Major Submissions to the Australian Pharmaceutical Benefits Advisory Committee involving Economic Analyses [
6]. The Manual recognises sources that include the Schedule of Medicare Benefits [
7], the Pharmaceutical Benefits Schedule [
8], and the Department of Veterans' Affairs Schedule of Fees [
9]. Unit costs of relevant services are presented in Table
1.
Table 1
Unit costs of health services associated with the ambulatory management of gestational diabetes mellitus.
Antenatal clinic visits | $28.75 | MBS item 16500 |
Physician clinic visits: | | |
initial | $119.35 | MBS items 110, 116 (consultant physician) |
subsequent | $59.75 | |
Dietician visits: | | DVA |
initial | $63.84 | DT-03 ($5.32*12) |
subsequent | $31.92 | DT-22 ($5.32*6) |
Diabetes educator | $31.92 | As for dietician subsequent visit (see above) |
Insulin therapy | $46.26 per week | Weighted average DPMQ for 11 PBS insulin items; Mean duration 6.4 weeks Intervention Group, 5.4 weeks Routine-Care Group |
Inpatient costing was only able to be performed for women and babies who were born at the Women's and Children's Hospital (WCH), Adelaide, Australia; the hospital which recruited the largest number of women (261/1,000; 26.1%) and which is typical of a large metropolitan tertiary care centre in Australia. The participating clinicians in the ACHOIS multi-centre trial had agreed to a common clinical management protocol. The trial began before computerised inpatient cost information systems became routinely available in the participating hospitals. From 1995–96 onwards, inpatient costs were obtained from Trendstar
® (McDonnell Douglas Information Systems), the WCH patient costing system, based on input from several feeder systems, including nursing dependency levels. In this system, inpatient separations are case mix-classified according to Australian-Refined Diagnosis Related Groups. Cost weights come from the National Hospital Cost Data Collection [
10] and include overheads. Inpatient costs for the baby were added to those of the mother.
Charges to women and their families were obtained by a questionnaire survey of a sample of 108 South Australian study participants (majority from the WCH) after funding for this became available, from January 1997 to June 2003. The themes covered in the questionnaire included time off work and costs for food, hospital parking, childcare, and blood sugar monitoring equipment. Data from general practitioners or community service providers were not collected because of research budgetary constraints. Costs were expressed in calendar year 2002 Australian dollars, adjusted by the Consumer Price Index (CPI) [
11]. Based on 2002 purchasing power parities, one Australian dollar would convert to 0.74 US dollars, 0.48 UK pounds or 0.66 Euros [
12].
The statistical analysis of the main ACHOIS trial with a sample size of 1000 women has been described elsewhere [
2]. A pragmatic judgment was made that the sample size for the economic evaluation should be determined by the limits of detection of differences in the primary outcome measures in the main trial. The power of the study to show differences in total health service costs was 7.5% and for patient changes 17.5%, assuming normality. As is common in health economic evaluation, the distribution of the costs per patient of managing gestational diabetes mellitus was skewed; hence bootstrapping (using 10000 resamples) was used to confirm the results of the analysis of variance [
13]. All occasions of service and health outcomes were adjusted by maternal age, race or ethnic group, and parity.
Discussion
The ACHOIS trial [
2] has demonstrated the clinical effectiveness of active treatment of women with mild gestational diabetes and this paper reports the cost-effectiveness of such treatment. Although a cost-consequence analysis was planned, the actual trial data allowed a credible cost-effectiveness ratio to be estimated, demonstrating that the form of an economic analysis often cannot be settled until data on effectiveness and cost are actually available [
15]. The ACHOIS trial also demonstrated that the health-related quality of life of the intervention mothers was better, both during the antenatal period and three months after birth [
2].
Our economic analysis used primary clinical outcome information and use of hospital services for all 970 women with a singleton pregnancy recruited to the ACHOIS trial. For assessing inpatient resource use, the relative differences in costs incurred by women and infants at the hospital contributing the largest number of women (n = 195) were assumed to be representative of those across the whole study. This representation was used because the trial began before computerised inpatient cost information systems became routinely available in the participating hospitals.
The size of this study was limited by the sample size of 1000 women in the ACHOIS trial and the small sample of women able to be assessed for charges to families. The power of the study to show differences was therefore low. Even with these limitations however, these data are of importance as there have been no previous reports of costs of treatment options for women with gestational diabetes from randomised trials.
It is likely that the general public in high-income countries such as Australia would find the reduction in perinatal mortality sufficient to justify the additional costs of $60,506, whether or not society places a larger value on a baby's life than on that of other members of the general public. Even incremented to current year costs, the figures would remain highly favourable. Indeed, at a value of $2,988, the incremental cost per life-year gained is highly favourable. By way of comparison, George
et al. [
16] found that historically the Australian Pharmaceutical Benefits Advisory Committee was unlikely to recommend a drug for government subsidy if the additional cost per life-year gained exceeded $86,154 and was unlikely to reject a drug for which the additional cost per life-year gained was less than $47,612 (2002 Australian dollar values).
The results suggest that being diagnosed with mild gestational diabetes mellitus and receiving the recommended care is not associated with any significant increase in the direct inpatient costs or postnatal length of stay, but is associated with an increase in the women's antenatal outpatient costs. This includes costs due to an increase in the number of visits to a physician, dietician and diabetes educator. The economic evaluation has been confined to in-trial costs and consequences. No modelling has yet been attempted to account for either costs or consequences beyond the end of the trial.
Acknowledgements
We are indebted to the women and their children who participated in this study; to SJ Alton, A Deussen, I Flight, E Griffith, J Lumley, A Thomas and L Watson for data collection, management and monitoring; to S Brown, K Bruggemann and P Moore for providing the in-patient cost data; and to M Ewens for administrative assistance with the manuscript.
The following persons and institutions participated in the ACHOIS Trial Group
Blacktown District Hospital, New South Wales: D. Chipps, R. Myszka, S. Hendon, M. McLean, H. Merker, J. Bradford; Bradford Royal Infirmary Maternity Unit, United Kingdom: D. Tuffnell, J. West; Caboolture Hospital, Queensland: M. Ratnapala, R. Hinton, D. Woodford, D. Cave, C. Armstrong, A. Vacca, P. Joubert, S. Mego, V. Heazelwood; Campbelltown Hospital, Sydney, New South Wales: H. Grunstein, S. Fleming, B. Marney; Flinders Medical Centre, Adelaide, South Australia: K. Harris, J. Ebert, R. Bryce, S. Judd, M. Keirse, C. Verco; General Infirmary, Leeds, United Kingdom: E. Ferriman, G. Mason, C. Lidelle-Johnson, J. Pearce; Hammersmith Hospital, London: M. de Swiet, A. McCarthy; Hervey Bay Hospital, Queensland: A. Lindberg, D. Ludwig, K. Wickremachandran; Lyell McEwin Hospital, Adelaide, South Australia: G. Dekker, P. Duggan, I. Hocking, W. Jeffries, S. Kennedy-Andrews, N. Kretschmer, H. Millar, J. Mowbray; Modbury Hospital, Adelaide, South Australia: C. Archer, C. Hughes, G. Matthews, M. Morton, N. Price, L. Purins, N. Tamlin, J. Sieben; Nambour General Hospital, Queensland: C. Cocks, M. Gregora, S. Hamwood, G. Pinn, C. Rutherford, C. Sheehan, T. Stubbs, V. Smith-Orr; Northern General Hospital, Sheffield, United Kingdom: S. Rutter, C. Bruce, R. Fraser; Queen Elizabeth Hospital, Adelaide, South Australia: B. Pridmore (deceased), W. Hague, P. Phillips, M. Sladek, S. Torr; Royal North Shore Hospital, Sydney: G. Burton, R. Hitchman, I. Kelso, A. McElduff, J. Morris; St. George Hospital, Sydney: C. Homer, G. Davis; Toowoomba Base Hospital, Queensland: P. Bridger, Y. Chadha, D. Gibson, M. Ratnapala; Townsville Hospital, Queensland: D. Watson, A. Rane, A. Robinson, J. Whitehall, S. Dunstone, R. Chadwick, A. Dederer, A. Lawrence; Women's and Children's Hospital, South Australia: C. Crowther, R. Burnet, A. McPhee, J. Robinson, A. Thomas, S. Alton, J. Hayton, J. Paynter, A. Deussen, J. Avery, S. Agett, D. Morris, B. Peat, C. Wilkinson, V. Coppinger, J. Dodd.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
All authors contributed to the study design, interpretation of the data and preparation of the drafts of the manuscript. In addition CC coordinated the trial and the collection of data. KW performed the data analyses. All authors read and approved the final manuscript.