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James Cook University Research puts new criteria for diagnosing gestational diabetes to the test

Changes to Australian guidelines for the testing of gestational diabetes have led to double the number of mothers being treated for the disease, according to researchers from James Cook University.

While this would appear to be good news for catching cases that might otherwise slip through, the jump in diagnoses hasn’t translated into improvements in key health outcomes, raising questions of whether it’s worth the added costs.

In 2015, the Australasian Diabetes in Pregnancy Society (ADIPS) adopted new criteria for diagnosing gestational diabetes mellitus (GDM).

As the name implies, GDM is a form of diabetes that develops during pregnancy. The condition caused by insulin-blocking hormones produced by the placenta, making it a temporary problem.

However the disease can have long lasting effects on both the mother and the child, including a higher risk of developing type 2 diabetes later in life and increased birth weights for the infant.

The new guidelines replaced recommendations that had been in place for just under 25 years, changing not only how expectant mothers should be tested for the condition, but how they were to be treated as well.

“The key differences included abolishing the glucose challenge test and introducing universal testing using the 75 gram glucose tolerance test for all pregnant women between 24 and 28 weeks of gestation,” says the study’s leader author Dr Holly Sexton from James Cook University College of Medicine and Dentistry.

The glucose challenge test was applied as a simple two-step procedure for mothers deemed to be a risk of GDM. It involves drinking a sugary solution followed by a blood test an hour or so later.

By comparison, the glucose tolerance test requires an overnight fast prior to testing, making it more sensitive to the diagnosis of insulin insensitivity. Guidelines advise all pregnancies to undergo testing.

Having a universal, sensitive method for diagnosing GDM seems like a winning strategy. Results from the 2008 Hyperglycemia and Adverse Pregnancy Outcomes Study also indicated this was the way to go.

The blinded analysis of more than 25,000 pregnant women from across the globe indicated a significantly increased risk of adverse outcomes for those whose elevated blood glucose levels fell below the current diagnostic threshold.

New guidelines have been in place for several years now, so researchers from James Cook University College of Medicine and Dentistry set out to check if they really did make a difference.

The study was supervised by AITHM member and JCU researcher Dr Clare Heal, Dr Kathleen Braniff gynaecologist and obstetrician, and JCU researcher Dr Jennifer Banks, consisting of an audit of clinical records from just under 1,400 pregnant women attending a Queensland regional hospital.

Roughly half of the births took place between March and August 2014, prior to the changes in guidelines. The other half occurred during the same period the following year, after the changes had been implemented.

Incidence of a positive GDM diagnosis between the groups was compared along with the types of treatment prescribed and pregnancy outcomes.

Prior to the change in criteria, 9.8 percent of mothers at the hospital were diagnosed with gestational diabetes. With new guidelines, 19.6 percent of mothers received a positive result.

“It was predicted that the new guidelines would significantly increase the number of women diagnosed due to the increased sensitivity of the diagnostic criteria,” says Sexton.

“Our study confirmed this prediction, and found that the number of women diagnosed with gestational diabetes doubled under the new criteria.”

Therapies also shifted as a result of the new criteria. Around 1 in 5 women with GDM had been prescribed insulin before the guideline changes, a figure that jumped to more than 1 in 4 in the wake of the amendments.

Similarly, a first-line diabetes medication called metformin was prescribed to around 18 percent of mothers with gestational diabetes. This also went up after the changed criteria, to just under a quarter.

Such changes aren’t free. Not only does broader testing require more pathology screening, prescribing more pharmaceuticals also adds costs. Whether benefits to the mother and child justify those costs remains a point of discussion.

On investigating the prevalence of emergency caesarean sections, increased birth weights, and low blood sugar in the newborn, the researchers failed to see an associated decrease in the rate of adverse outcomes.

The study isn’t a final word on the pros and cons of the new ADIPS guidelines. But it does highlight potential limitations which warrant further investigation.

“Our study had the limitation of being conducted in a small centre, and the sample size was not large enough to look adequately to see if there was any change in some of the less prevalent adverse outcomes attributed to diabetes in pregnancy,” says Sexton.

Future studies replicating these results could help consolidate the findings, and show whether they reflect a widespread trend.

“Once clear patterns are more evident, it may be pertinent to review the guidelines and institute change where indicated,” says Sexton.

Professor Clare Heal

Dr Jennifer Banks

Dr Kathleen Braniff


Publication

Sexton, H. , Heal, C. , Banks, J. and Braniff, K. (2018), Impact of new diagnostic criteria for gestational diabetes. J. Obstet. Gynaecol. Res., 44: 425-431. doi:10.1111/jog.13544


Contacts

Holly Sexton

E holly.sexton@my.jcu.edu.au

Dr Clare Heal

E clare.heal@jcu.edu.au

Dr Jennifer Banks

E jennifer.banks2@jcu.edu.au

Dr Kathleen Braniff

P  (07) 4968 6000

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