Diagnoses Gestational diabetes during pregnancy. Gestational diabetes is a potentially serious pregnancy condition that can harm you and your baby. However, globally, there is a significant lack of clarity about how and when gestational diabetes should be diagnosed. This includes the different testing procedures, various criteria used to test, and disparate criteria used to diagnose.

This lack of clarity has resulted in the probability of a gestational diabetes diagnosis increasing or decreasing based on where a pregnant woman lives, rather than any specific aspect of her health or wellbeing. For example, in Australia, we have seen a significant rise in women diagnosed with gestational diabetes. This is due to changes in testing practices.

You may think that’s great, as more women and babies are being kept safe. However, the reality is that the change to Australian testing procedures was not evidence-based. It was rejected by leading medical authorities.  So the questions we must ask are: Why this change occurred? What impact it has had on women and their babies?

Why did the Australian testing methods change?

In 1998, they formed the International Association of Diabetes and Pregnancy Study Groups (IADPSG) to facilitate international collaboration regarding gestational diabetes. In 2008, the IADPSG convened an international conference. During this, a consensus panel of ten member groups reviewed the HAPO study. (a big study that looked at the effect of high blood sugar on pregnant women). In the report developed, as a result, the IADPSG stated:

• The report represents the opinions of individual members, not the position of the organisations they represent,
• The recommendations are based on the panel members’ opinions because the information from appropriately designed clinical trials was unavailable.

While the panel examined research, the report was essentially an opinion piece – recommendations were based on the opinions of members of the panel because sufficient information was not available to develop a definitive, research-based position statement.

Many countries rejected the IADPSG’s recommendations. Australia did not. Three of the IADPSG’s recommendations continue to have lasting ramifications on the diagnosis and treatment of gestational diabetes in Australia:

1. Rather than testing only women with known risk factors, the IADPSG recommended testing all women for gestational diabetes.
2. Rather than the two-step glucose challenge, followed by an oral glucose tolerance test (OGTT), the IADPSG recommended all women be tested using a one-step 75 g OGTT.
3. The IADPSG recommended the threshold levels of blood glucose used for diagnosing gestational diabetes be reduced.

As a result of these recommendations, the IADPSG has been widely criticised for contributing to the medicalisation of healthy pregnancies, with potentially harmful implications on women’s quality of life.

The effect of lowering the threshold measurements for gestational diabetes

Changing how gestational diabetes is diagnosed has led to women previously considered healthy being included in the group for unhealthy women and classified as high-risk pregnancies. In medicine, this phenomenon is called stage migration.

In addition, while these women add to the number of women diagnosed with gestational diabetes, they do not add to the number of women or babies who experience adverse outcomes. As the HAPO study showed, blood glucose levels at the lower end have lower complication rates.

Think of it like this. Suppose you have 100 women with an elevated blood glucose of 5.6 mmol/L+, and one experiences an adverse outcome, which is a rate of 1 in 100 or 1%.

Now add another 100 women to the group with blood glucose levels below 5.6 mmol/L. None of whom have adverse outcomes.

If you use this group of 200 to measure the rate of adverse outcomes, you now have one incidence in 200 or 0.5% for adverse effects.

We could say, look at that! The rate of adverse outcomes has HALVED because of better testing. However, this isn’t the truth. The ‘improvement’ is artificial. We added women who were previously considered healthy to the group.

Diagnoses Gestational diabetes: The benefit of testing

Research seems to have conclusively shown that women with overt gestational diabetes (that is, very high blood glucose levels) and their babies are at significant risk of adverse outcomes. However, treating these women appears to improve results.

In 2005, an Australian trial was conducted of 1000 women diagnosed with gestational diabetes using the Carpenter–Coustan two-step criteria. The researchers randomly assigned 490 women to receive interventions, including dietary advice, blood glucose monitoring and insulin therapy. The remaining 510 women received only routine care.

Within the intervention group, there were significantly lower rates of severe complications during pregnancy and after birth (perinatal complications were 1% versus 4%). These complications were defined as death, shoulder dystocia, bone fracture and nerve palsy.

These results form a sound basis for testing women at risk of developing gestational diabetes. Therefore treating women with overt gestational diabetes is a valid practice to help ensure the well-being of women and babies.

But isn’t it better to be safe than sorry then?

Despite the HAPO study showing correlations between higher blood glucose levels and significant complications, we still have no conclusive evidence that screening women who do not have risk factors lead to improved outcomes for women and babies.

Some studies have found improved outcomes for women and babies by testing all women in a study group, irrespective of risk factors. Other studies have found no benefit. However, in 2021, the results of a large trial involving 23,792 women were published.

The women were randomly assigned to two groups. They tested a group of women using the one-step OGTT test, and the other half using two-step criteria. Not surprisingly, the number of women diagnosed with gestational diabetes in the one-step group was almost twice the number diagnosed using two-step criteria.

However, despite the higher number of women in the OGTT group, the rates of adverse outcomes in the two groups were the same. There was no difference in the number of:

• infants who were large for gestational age
• caesarean deliveries
• women diagnosed with gestational hypertension or preeclampsia
• severe perinatal outcomes (stillbirth, neonatal death, shoulder dystocia, bone fracture or nerve-related birth injury)

In short, diagnosing more women with gestational diabetes did not result in more women or babies being ‘saved’ from severe outcomes. Therefore, it provides conclusive evidence that using a lower blood glucose level to diagnose women with gestational diabetes offers no benefit.

The harm of over-testing

Even though the Australasian Diabetes in Pregnancy Society (ADPS) endorses the IADPSG approach, The Royal Australian College of General Practitioners has refused. Their concerns can essentially be summed up in a risk versus benefit analysis.

On the one hand, diagnosing and treating a woman with overt gestational diabetes has been shown to have benefits. But, on the other hand, the reality is that an unnecessary or invalid diagnosis of gestational diabetes contains a considerable risk for potential harm. Harm like those created by dropping the blood glucose thresholds.

For women, this can include life disruptions of additional monitoring, unnecessary anxiety and worry for the welfare of their baby, a risk of more invasive forms of delivery, fewer options offered for birth, and being induced sooner if overdue (40 weeks + 6 days versus 40 weeks + 7 to 12 days).

There is also the potential for harm to the infant from restricted diets, insulin use during pregnancy, and an increased risk of neonatal hypoglycaemia.

Diagnoses Gestational diabetes: The take-away message

There is no evidence of value in universally testing all pregnant women. In addition, diagnosing women using the IADPSG one-step test is flawed at best and harmful at worst.

It is time that Australia acknowledged the stance of The Royal Australian College of General Practitioners against the IADPSG approach. In addition, Australia needs to revisit its testing criteria for gestational diabetes based on recent research. It is the only way to ensure testing offers the maximum benefit and minimal harm to women and their babies.

Published 17th June 2022