Previous guidelines released in 2014 had been criticised by the RACGP and others, with many citing concerns that included risk of overdiagnosis. However, the consensus at the time was that the lower glucose thresholds were justified to improve foetal outcomes.
The new guidelines have “a slight but significant elevation of glucose thresholds to diagnose GDM – to allow better targeted therapy for women identified as high risk from their GDM,” says Dr Gary Deed, chair of the RACGP diabetes specific interest group.
Specifically, GDM should be diagnosed using one or more of the following criteria during a 75 g two‐hour pregnancy oral glucose tolerance test (POGTT):
This time around, the College has endorsed the guidelines – as have 10 other peak bodies including Diabetes Australia and RANZCOG.
Dr Matt Hare, an endocrinologist, clinician researcher and president of the Australasian Diabetes in Pregnancy Society (ADIPS) who co-led the new guidelines, says the process included a thorough review of the evidence.
“But because there isn’t clear-cut evidence regarding a single best way to screen and diagnose GDM, it necessitates a consensus-based approach, and so we had an extensive process of engaging with key health professional stakeholders, as well as consumer groups,” Dr Hare said.
More evidence has come to light in the decade since the last guidelines were published – along with growing awareness of the impact on health services and pregnant women, both from a psychosocial perspective, as well as potential over-intervention relating to treatment at lower thresholds.
There’s always going to be pros and cons, wherever you draw the cut-offs, he notes.
“If the diagnostic threshold is lower, you’re identifying women who are still at increased risk of adverse pregnancy outcomes compared to someone without GDM,” he says. “But that relative increase in risk is smaller, which means their potential to benefit from the extra management and treatment is a little bit less than someone who’s diagnosed at a higher threshold.”
Dr Deed concurs that there is a continuum of risks.
“The more recent data has shown that women in the margin between the previous criteria and new criteria did not have as severe neonatal outcomes,” he says.
But the GEMS trial showed that in the subgroup whose OGTT results fell between the lower and higher glycaemic criteria, treatment for GDM was associated with significantly reduced risk of large for gestational age babies and pre‐eclampsia. However, treatment at these lower glycaemic thresholds was also associated with greater health service use, and an increased risk of small for gestational age babies and early term birth, the study found.
Given there’s no ‘absolute level’ where hyperglycaemia is without risk, it’s particularly important to support women in the “intermediate zone” to address modifiable risk factors that improve pregnancy outcomes, Dr Deed says.
“So even women on the ‘marginal’ levels need advice on lifestyle and diet to assist their pregnancies and help their babies. They may not need intensive medical interventions such as insulin,” he says.
ADIPS advises that current care or management of women already diagnosed with GDM should not change on the basis of their oral glucose tolerance test results.
“Those clinical decisions should be individualised and based around what the blood glucose monitoring is showing, what the ultrasounds are showing in terms of foetal growth — and then care decisions can be based on that,” Dr Hare says.
“Even under the old criteria, women with GDM are at increased risk of developing type 2 diabetes in later life. They should still be offered appropriate supportive care to help prevent type 2 diabetes onset in the future, and still should be offered routine diabetes screening,” he adds.
Dr Deed says postnatal follow up is key.
“The pragmatic advice is that any women previously diagnosed should have identical follow up as before – that is postnatal glucose testing as per the RACGP and ADIPS guidelines,” he says.
In an accompanying FAQ, ADIPS says “self-monitored blood glucose levels (BGLs), prior pregnancy outcomes, and clinical context should all be considered. Decisions to reduce the frequency of blood glucose monitoring or to change treatment, follow-up or model of care, should be based on current BGLs and the whole clinical context, rather than the initial diagnostic OGTT results.”
The new guidelines emphasise early detection of overt diabetes in pregnancy (DIP), as distinct from GDM, Dr Deed says, adding that by definition DIP has levels of glycaemia equivalent to T2DM levels.
“Early detection and management of these high risk women during pregnancy is clearly beneficial,” Dr Deed says, noting that GPs will play a key role in identifying those at high risk.
Dr Hare points out that in the updated recommendations, any woman with one or more risk factors for diabetes in pregnancy should be offered HbA1c in early pregnancy.
“The recommendations only suggest doing an early oral glucose tolerance test for women who have a history of previous gestational diabetes, or for whom that HbA1c result comes back in a borderline range,” Dr Hare says.
Diabetes screening recommendations in pregnancy
First Trimester – Include HbA1c when booking bloods for women at increased risk of hyperglycaemia
10-14 weeks (acceptable up to 20 weeks) – POGTT in women WITH previous GDM or with early pregnancy HbA1c 6.0-6.4
24 – 28 weeks – POGTT for all women not already diagnosed with DIP or GDM, regardless of perceived risk.
Overt diabetes in pregnancy should be diagnosed at any time in pregnancy if one or more of the following criteria are met:
Dr Hare emphasises the importance of holistic person-centred care for women at risk of diabetes in pregnancy. “The guideline is a standard recommendation regarding screening that will require some degree of adaptation to best suit individual women and their preferences.”
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