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CONTINUING controversy surrounding the diagnostic thresholds for gestational diabetes is presenting problems for GPs, says a leading endocrinologist.
Professor David McIntyre, director of endocrinology and obstetric medicine at Brisbane’s Mater Health Services, said there was “fairly broad consensus and some vocal dissent” about the new lower thresholds for gestational diabetes (GDM).
“That does make it exceedingly difficult for GPs. I know at the moment there are laboratories putting [both the] old criteria and the new set of criteria on their reports, which means that a woman can both have GDM and not have GDM … so it’s getting a bit ridiculous.”
Professor McIntyre was commenting on two “For debate” articles published in the MJA — one questioning the statistical basis of the new risk threshold and another suggesting that the implementation of new treatment targets was premature. (1), (2)
The articles follow the Australian Diabetes in Pregnancy Society’s (ADIPS) adoption of the WHO diagnostic criteria for gestational diabetes, which is in line with the International Association of Diabetes and Pregnancy Study Groups’ threshold consensus. (3)
Writing in the MJA, Associate Professor Michael d’Emden, director of endocrinology and diabetes at Royal Brisbane Women’s Hospital, suggested some minor modifications to the criteria could more accurately identify patients whose babies were large for gestational age.
In the other MJA article, Dr Dev Kevat of Monash University’s school of public health, and coauthors, said lowering the treatment targets for gestational diabetes to 5.0 mmol/L fasting, 7.4 mmol/L at 1 hour and 6.7 mmol/L at 2 hours after meals was premature.
Dr Kevat said although ADIPS guidelines had described these lower targets as “suggestions”, many doctors would be looking to these targets for direction. “While there may be benefits, lowering treatment targets may cause a number of harms including increased risk of hypoglycaemia in pregnant women, greater medicolegal risk for health practitioners, and heavier economic costs for the health system”, he wrote.
Professor McIntyre, a council member of ADIPS and a former president, said the MJA paper had “over-interpreted” the aim of the treatment targets, which ADIPS had acknowledged required further research.
“Most people would say that exactly which numbers one should aim for in treatment needs to be tempered by the individual woman and her baby and the clinical situation”, he told MJA InSight.
Professor McIntyre said concerns about overtreatment were valid. “You don’t want to be overtreating people just to try to achieve a notional set of numbers. But on the other hand … in our clinic we have been treating people to an overall fasting glucose target of 5 mmol/L for several years without ever producing an episode of severe hypoglycaemia”, he said.
Professor Stephen Colagiuri, professor of metabolic health at the University of Sydney and a co-chair of the 2011 WHO committee that recommended the adoption of the new criteria, also said the points raised in the MJA about treatment targets were valid. (4)
“They are guides, but as pointed out … there may be medicolegal issues if you don’t aim for those and something happens, as does unfortunately from time to time, with the outcome of a pregnancy. So this is a very controversial area … and the evidence to support [treatment targets] is not as strong as those for the diagnostic criteria.”
Professor Colagiuri said there was broad agreement on the new diagnostic criteria regarding the recommendation to use the 75 g oral glucose tolerance test to assess glucose tolerance status. Those women meeting the criteria (blood sugar level >= 7.0 mmol/L fasting and/or >=11.1 mmol/L at 2 hours) for diabetes should be diagnosed with diabetes rather than being labelled as having gestational diabetes. GDM is now applied to women with levels below diabetes but above “normal”.
However, he said the decision to lower the fasting glucose level to 5.1 mmol/L for a diagnosis of GDM had proved to be controversial.
“WHO recognises that the evidence is low, but [adopted these criteria] for the sake of international consensus so that we can move forward and try to sort out these controversies”, Professor Colagiuri said.
“[The d’Emden article] makes a good point … there are some issues with the outcomes that have been selected to determine these new criteria. There was debate [at the WHO] as to whether to adopt the 1.75 times risk of outcomes or two times risk, but nevertheless the group decided to go with the 1.75 times.”
Earlier this year, the Royal Australian College of General Practitioners (RACGP) decided not to endorse the ADIPS recommendations, preferring to support the existing recommendations until further evidence became available. (5)
Professor Colagiuri said the RACGP’s decision not to endorse the new diagnostic criteria was “unfortunate”.
“We are dealing with a continuous variable — there is no magic point at which you can say somebody is normal or abnormal”, he said.
“It may be in 5 years’ time we decide that these criteria are still as good as anything … or maybe they need to be tweaked.”
1. MJA 2014; 201: 209-211
2. MJA 2014; 201: 204-207
3. ADIPS 2014: Consensus guidelines for the testing and diagnosis of gestational diabetes mellitus in Australia
4. WHO 2013: Diagnostic criteria and classification of hyperglycaemia first detected in pregnancy
5. RACGP: General practice management of type 2 diabetes 2014–2015
(Photo: Shutterstock)
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As Prof Colagiuri says, glycaemia is a continuous variable, and the HAPO study (1) showed us that it has a linear relationship with birthing outcomes. Any diagnostic thresholds are necessarily going to be arbitary, and therefore it is unsurprising that continue to be controversial.
Rather than continuing to search for a universally-accepted definition of ‘abnormal’ we should shift to thinking of glycaemia in the same way we consider other risk factors of a continuous nature (like weight and blood pressure), where lower values confer less risk and higher values higher risk.
Lower cutoff points, as proposed by ADIPS, IADPSG and the WHO, allow us to recognise a woman’s risk and intervene as appropriate. Where borderline or mild hyperglycaemia is a woman’s only obstetric risk factor, treatments will clearly be different from where hyperglycaemia is present in conjunction with obesity, high blood pressure, or abnormal fetal growth velocity. As Rural Doctor says, clinical judgement is still required. That said, even in women with a fasting glucose of <5.3mmol/L, treatment has been demonstrated to reduce risk of fetal overgrowth, shoulder dystocia, c-section and hypertensive disorders. (2)
1. http://www.nejm.org/doi/full/10.1056/NEJMoa0707943
2. http://www.ncbi.nlm.nih.gov/pubmed/19797280
The system is too simplistic.
Our first injunction is “Do no harm”. Because we have a large range of diseases with a common label “diabetes” we have some women who will have harm caused to them by these criteria, and others who will have harm done to them if we don’t use these criteria.
I am thinking specifically about MODY 2, where the effect on the fetus varies according to its own inheritance, which we cannot test.
This pronouncement about treatment of all pregnant women with raised fasting blood sugars has the same problem as every Guideline – it will be taken as Law, instead of Advice.
I try to teach people to think for themselves and not slavishly follow guidelines – they may come to the same conclusion, or they may decide the advice is inappropirate in the case before them.