In reply: Taylor welcomes a strong evidence base for clinical practice, which is echoed by d’Emden and colleagues. However, their strong support for the current Australian diagnostic criteria for gestational diabetes mellitus (GDM) is surprising, given that these criteria are the product of an “Ad Hoc Working Party” report.1 This guideline, published in 1991, clearly acknowledged a lack of strong evidence and advocated criteria that were based on best available rounded values for the 95th centile of venous plasma glucose (VPG) levels in the fasting state (5.5 mmol/L) and 2 hours after a 75 g glucose load (8.0 mmol/L) — values that had been published in an unreferenced overview of Australian and European data.1 It advocated future prospective studies, such as those which form the basis of the International Association of the Diabetes and Pregnancy Study Groups (IADPSG) recommendations.2 Contrary to d’Emden et al’s assertions, the 1991 fasting and 2-hour VPG level cut-offs are misaligned. Contemporary data from the 2120 Australian women in the Hyperglycemia and Adverse Pregnancy Outcome study, using the 75 g oral glucose tolerance test, show that 5.5 mmol/L lies at the 98th centile for fasting VPG level, while 8.0 mmol/L corresponds to the 91st centile for 2-hour VPG level (own unpublished data). A recent summary of ambulatory blood glucose monitoring in pregnancy suggested even tighter normative values, with the 97th centiles for fasting blood glucose level (BGL) (4.8 mmol/L) and 2-hour post-meal BGL (6.6 mmol/L) being lower than previous guesstimates.3
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