Gestational diabetes diagnoses higher with one-step approach

Morgan Liotta

19/03/2021 4:04:37 PM

But crucially, the results of a new study investigating the two screening methods found neither led to significantly different clinical outcomes.

Pregnant woman holding belly
The RACGP first recommends the two-step process to diagnosis of gestational diabetes.

A randomised trial of 23,792 women that compared two approaches to screening and diagnosis of gestational diabetes, recently published in The New England Journal of Medicine (NEJM), has shown the one-step approach achieves more diagnoses (16.5%) than with the two-step approach (8.5%).
However, the extra diagnoses did not lead to any significant differences in the primary outcomes relating to perinatal and maternal complications.
Instead, similar or non-significant differences were observed in perinatal outcomes, with respective results for one-step versus two-step approaches being:

  • large-for-gestational-age infants, 8.9% vs 9.2%
  • perinatal composite outcome, 3.1% vs 3%
  • gestational hypertension or pre-eclampsia, 13.6% vs 13.5%
  • primary caesarean section, 24% vs 24.6%
Dr Gary Deed, Chair of RACGP Specific Interests Diabetes told newsGP the study offers valuable findings for screening and diagnosis.
‘The study was powered to detect the differences in approaches, despite unequal numbers in the one-step versus two-step diagnostic process,’ he said.
Professor Jenny Doust from the University of Queensland’s School of Public Health agrees, but says there is still some uncertainty around the results.

‘This trial doesn’t have enough power to establish non-inferiority, even with the 23,792 women enrolled,’ she told newsGP.
‘This may be technically correct, but this shouldn’t be used to dismiss the results of the trial, and it demonstrates how many women would need to be screened to show a difference in outcomes.’
Given the trial shows no increase in adverse outcomes from a two-step approach, GPs using it do not need to be concerned, according to Dr Deed.
‘Both approaches are likely to be used in Australia for some time yet,’ he said.
International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria to detect gestational diabetes comprise:
  • the one-step approach – a single fasting two-hour 75 g oral glucose tolerance test, with blood sugars checked at fasting, one hour, and two hours. Diagnosis is confirmed if one or more values is positive
  • the two-step approach – involving a non-fasting one-hour 50 g glucose challenge test. If the result is positive, the test is followed by a fasting three-hour 100 g oral glucose tolerance test, with values checked at fasting and one, two, and three hours. 
The RACGP’s Management of type 2 diabetes: A handbook for general practice (Diabetes handbook), along with other guidelines, recommends implementation of the IADPSG criteria, despite being met with some controversy, but first recommends retaining a two-step process.
The Diabetes handbook notes important differences in the IADPSG guidelines as ‘universal testing of all women not already diagnosed with diabetes in pregnancy, and a one-step diagnostic framework with a changed glucose threshold, versus the previous two-step process’.
The handbook also cites the importance of GPs being aware of their local obstetric service’s diagnostic criteria, and also supporting and managing patients ‘in a manner congruent with their specialist team guidelines, to avoid conflict and patient confusion’.
According to the NEJM study, consensus is lacking about which two recommended screening approaches for gestational diabetes should be used.
‘Although there is clear guidance on both approaches in recognition of the different recommendations across Australia, the handbook clearly states the two different diagnostic routes and to be mindful of such when implementing clinical care,’ Dr Deed, also clinical lead on the Diabetes handbook, said.
‘This new evidence from the NEJM study is emerging and important, but until we can be entirely certain, the RACGP adheres to our current position, as outlined in the Diabetes handbook, and our current reasoning.’
However, the study should influence changes in the gestational diabetes guidance and processes that were made in some areas as a result of the COVID-19 pandemic.
‘In some states, a two-step process was used to reduce the proportion of women needing to go to a laboratory or clinic for three hours in their pregnancy,’ Dr Deed said. ‘That change is now being revised, but some are arguing to retain.’
Studies are currently underway on the impact of COVID-19 on screening for gestational diabetes.
‘Further studies are also emerging that may question the one-step diagnostic process as an agreed diagnostic route,’ Dr Deed added.
‘It is imperative to be mindful of this emerging evidence, as distress to women in pregnancy with unnecessary emotional burden associated with diagnostic labelling and the economic/health burden are not inconsiderable.’
Management of type 2 diabetes: A handbook for general practice is available on the RACGP website.
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