Risk of undetected cases of gestational diabetes mellitus during the COVID‐19 pandemic

Siru et al have raised potential concerns about the strategy recommended by the Australian Diabetes Society and other peak bodies to diagnose gestational diabetes (GDM) during the COVID-19 pandemic (1).  In their study, 46% of subjects diagnosed with GDM had fasting blood glucose level (FBG) < 4.7mmol/l but raised post-load BGLs and would be missed by the ADS-recommended strategy.  The authors suggest that this exposes women and their newborns to significant risks with the potential for significant harm. No outcome data is provided to justify these assertions. 

The evidence from HAPO suggests these women do not have increased rates of pregnancy-associated complications.  The subgroups with the highest odds ratios (OR) for large for gestational age (LGA) had elevated fasting and any elevation of post-load BGLs (OR>3) whereas subgroups having only an elevated fasting or post-load glucose level had a considerably lower OR, equivalent to the diagnostic threshold for GDM of 1.75 (2). Further, women with an FBG < 4.5mmol/l had low rates of some complications irrespective of their post-load BGLs (3).  A subsequent analysis of 6128 subjects from 5 HAPO centres did not observe any increase in pregnancy-associated complications in women having an FBG < 75th centile [4.6mmol/l (4)].  A recent analysis of 5974 women in HAPO assessed the ADS-recommended COVID-19 GDM strategy and reported no increase in any complication (5).  There were fewer cases of pregnancy-associated hypertension and Caesarean section, with similar rates of LGA and neonatal hypoglycaemia.    

These data provide reassurance. There is no evidence of harm. When this strategy is used, women with a FBG<4.7mmol/l are spared being labelled with GDM and do not require education, monitoring, more frequent follow-up or transfer to specialist services, freeing up valuable health care resources. Importantly, they will not be advised to inappropriately restrict their dietary intake or commence therapy with insulin or metformin with the potential for harm.  An initial FBG would be an ideal initial screening test eliminating the need for a POGTT in the majority of women, identifying a smaller group of women at risk of pregnancy-associated complications where management can be more appropriately targeted.

References:

1. Siru R, Conradie HJ, Gillett MJ et al Risk of undetected cases of gestational diabetes mellitus during the COVID‐19 pandemic. Med J Aust 2020; 213 (7): 335-335. https://www.mja.com.au/journal/2020/213/7/risk-undetected-cases-gestational-diabetes-mellitus-during-covid-19-pandemic
2. Metzger BE, Dyer AR. Comment on d’Emden: Do the New Threshold Levels for the Diagnosis of Gestational Diabetes Mellitus Correctly Identify Women at Risk?  Diabetes Care 2014;37:e43-44
3. Metzger BE, Gabbe SG, Persson B, et al.; International Association of Diabetes and Pregnancy Study Groups Consensus Panel. International Association of Diabetes and Pregnancy Study Groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy.
4. McIntyre HD, Gibbons K, Sacks D et al. Using fasting plasma glucose to identify women with gestational diabetes at low risk of complications. Available at: https://www.easd.org/virtualmeeting/home.html#!users/58812
5. McIntyre HD , Gibbons KS, Ma R.C.W. et al.  Testing for gestational diabetes during the COVID-pandemic. An evaluation of proposed protocols for the United Kingdom, Canada and Australia. Diab Res Clin Practice 2020 July 30. Available on-line at https://doi.org/10.1016/j.diabres.2020.108353