1.3.4.1 International studies on the clinical and cost implications of the new IADPSG approach
In 2008, the HAPO study investigated whether maternal hyperglycaemia less severe than that in diabetes mellitus is associated with increased risks of adverse pregnancy outcomes (Test, 2008). A total of 25,505 pregnant women at 15 centers in nine countries were involved. The HAPO study found strong, continuous associations of maternal glucose levels below the diagnosis of diabetes with increased birth weight and increased cord-blood serum C-peptide levels. This indicated that adverse maternal and neonatal outcomes appeared across a wider range of maternal glucose levels than previously thought. Having reviewed the result from the HAPO study, in 2010, the IADPSG Consensus Panel recommended a major change in GDM screening, promoting a one-step 75g OGTT for all pregnant women from 24th to 28th week of gestation with lower OGTT threshold values than had been used previously (Panel, 2010). Under the new regimen of one-step universal screening approach, GDM diagnosis is confirmed if there is at least one abnormal value registered from the three that have been measured (fasting glucose ≥5.1 mmol/l, 10 mmol/l at 1 hour, and 8.5 mmol/l at 2 hours). In line with this, the new IADPSG approach was expected to substantially increase the GDM incidence, potentially doubling or tripling the incidence (Panel, 2010).
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One issue with the IADPSG criteria was that it is only based on observational datasets, including the large observational HAPO study (Test, 2008). No randomised controlled trial has been conducted to test the effectiveness of the IADPSG approach, which prevents a definitive conclusion of the superiority of IADPSG (Cundy et al., 2014). However, following the observational study of HAPO (Test, 2008), there have been increasingly more observational studies (i.e., case-control studies) undertaken supporting the notion that the IADPSG is clinically more effective (Lapolla et al., 2011; Benhalima et al., 2013). These retrospective studies have found that the women classified as normal in accordance with the old criteria but re- classified as GDM by the IADPSG criteria (i.e., new GDM women) had significantly higher incidences in clinically important adverse outcomes (e.g., caesarean section delivery, large for gestational age, shoulder dystocia). This implied that diagnosing and treating these women would have improved the outcomes. In China, the conducted observational studies also showed the IADPSG approach was more clinically effective (Shang & Ma, 2011; Wei & Yang, 2011; Lu et al., 2012; Jiang et al., 2013).
Two recent studies evaluated the cost-effectiveness of the IADPSG one-step approach compared with the two-step approach currently used in many countries (Mission et al., 2012; Werner et al., 2012). Mission et al. (2012) found that the IADPSG approach was more expensive and more effective but cost-effective at $61,503/ quality-adjusted life year (QALY). However, Werner et al. (2012) suggested the IADPSG recommendation was cost-effective only when post-delivery care reduced diabetes incidence. Thus far, no cost-effectiveness study has been conducted in China. Vandorsten et al. (2012) have concluded that available studies do not provide clear evidence that a one-step approach is more cost-effective compared with the current two-step approach.
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Concerns over the costs and cost-effectiveness are among the key reasons that countries hesitate to adopt the IADPSG approach. The NIH panel stated that they were particularly concerned about the increase of corresponding costs and interventions by adopting the IADPSG approach (NIH, 2013). The increased costs are comprised of the increased diagnosis costs by conducting OGTT among all pregnant women, and the increased healthcare costs by treating the additional women diagnosed as GDM. If, as concluded by all the observational studies, the IADPSG approach is more clinically effective, it will be necessary to spend the additional treatment expenditure on these GDMs. However, there is still a need to explore whether the diagnosis costs of conducting the OGTT could be reduced without compromising the clinical effectiveness, which would improve the cost- effectiveness of the IADPSG approach.
1.3.4.2 Chinese studies on the clinical and cost implications of the new IADPSG approach
The new IADPSG recommendation was based on the HAPO study that did not include data from China. To explore the applicability of the approach to China, several Chinese studies investigated the clinical effectiveness of the new IADPSG approach in comparison with other approaches. These are summarised below.
Three studies (Shang & Ma, 2011; Lu et al., 2012; Cai & Yang, 2012) compared the IADPSG one-step universal approach with the previous two-step universal approach for GDM. Shang & Ma (2011) and Lu et al. (2012) evaluated the clinical outcomes of the "over-diagnosed" GDM cases that were picked up by the IADPSG criteria but not by the previous two-step tests. Shang & Ma (2011) divided the additionally diagnosed GDM cases into treatment and non-treatment group, and found the treatment group had better clinical outcomes, indicating it was important to diagnose
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and treat these additional GDM women. Lu et al. (2012) compared the outcomes of the "over-diagnosed" cases with non-GDM women and found that, if left untreated, the additionally diagnosed GDM cases were characterised by significantly higher rates of maternal and neonatal complications than women without GDM. Both findings suggested that IADPSG approach was clinically more effective in China. The other study by Cai & Yang (2012) was biased in study design. It found that if treatment were provided, the GDM diagnosed against the IADPSG criteria had significantly fewer adverse outcomes than GDM women diagnosed with the older criteria, thus leading to the conclusion that IADPSG criteria was better. However, this might simply have transpired because the GDM cases diagnosed by the IADPSG criteria were milder cases due to reduced OGTT thresholds.
Jiang et al. (2013) compared the one-step 75g OGTT universal approach using the IADPSG cut-offs (reduced thresholds) and the older cut-offs. The additional women who were diagnosed by the IADPSG cut-offs (8.14% GDM incidence) but not by the older cut-offs (4.57% GDM incidence) were divided into treatment and non- treatment groups. It was shown that the maternal and neonatal outcomes were significantly better in the treatment group, thereby suggesting that the reduced cut- offs of the IADPSG criteria improved clinical outcomes. However, no published cost or cost-effectiveness study for the IADPSG screening approach in China has been identified.