One in three mothers born in Southern and Central Asia is told she has gestational diabetes. The definition just changed.

If you were born in India, Pakistan, Sri Lanka, Bangladesh or Nepal and gave birth in an Australian hospital in 2023-24, there was a one in three chance you were diagnosed with gestational diabetes. For a woman born here, the chance was one in six.

Those are the Australian Institute of Health and Welfare’s own figures, published in its Diabetes: Australian facts report and updated on 27 May 2026. For 2023-24, among women aged 15 to 49 who gave birth in an Australian hospital, the incidence of gestational diabetes for those born in Southern and Central Asia was 33.1 per cent. For Australian-born women it was 16.0 per cent. The institute puts it plainly: women born in Southern and Central Asia were 2.1 times as likely to be diagnosed. That category takes in the countries above and others, including Central Asia, and the institute publishes no separate South Asian figure.

Since then, the test itself has been marked differently.

What changed in gestational diabetes criteria, and when

In June 2025 the Australasian Diabetes in Pregnancy Society published new consensus recommendations for screening, diagnosing and classifying the condition. The paper, led by Arianne Sweeting, appeared online in the Medical Journal of Australia on 23 June 2025.

The society raised the numbers that define a positive glucose tolerance test. Under the 2014 criteria, a fasting reading of 5.1 mmol/L or above, a one-hour reading of 10.0 or above, or a two-hour reading of 8.5 or above meant a diagnosis. Under the 2025 criteria the fasting cut-off is 5.3, the one-hour cut-off is 10.6 and the two-hour cut-off is 9.0. The upper bounds, 6.9 fasting and 11.0 at two hours, are unchanged.

Small numbers, large consequences. A fasting result of 5.2 met the old definition and does not meet the new one.

Victoria has moved. Safer Care Victoria records that all public and private pathology services in the state agreed to change to the new criteria as of 4 August 2025. Whether the pathology provider your service uses in another state has done the same is a question to ask at the clinic.

Why the bar was raised

The society’s reasoning is about who benefits from treatment. The 2014 thresholds followed an international consensus group’s reading of a large study of glucose levels and pregnancy outcomes, with the line set where the odds of complications were 1.75 times those at the study’s average glucose level. The 2025 thresholds move that line to odds of 2.0. The paper cites a New Zealand trial that found the lower criteria more than doubled the prevalence of the condition compared with the New Zealand guidelines, 15.3 per cent against 6.1 per cent.

Fewer diagnoses, then, by design.

At the same time the society asks clinicians to look earlier. Women with risk factors who have not had an HbA1c test in the past 12 months should have one at their first antenatal visit. Those with a previous history of gestational diabetes, or an early HbA1c of 6.0 to 6.4 per cent, should be tested before 20 weeks.

The paper’s table of risk factors lists previous gestational diabetes, obesity, overweight, family history of diabetes, age from 30, polycystic ovary syndrome, hypothyroidism, a history of adverse pregnancy outcomes such as a large baby, pre-term delivery, congenital anomaly, stillbirth or pregnancy-induced hypertension, and having given birth more than once. Ethnicity does not appear on it, which is worth knowing before anyone tells you that the new guideline singles out South Asian women. It does not.

What sits underneath the AIHW number

The 33.1 per cent did not arrive from nowhere. Research led by Wubet Takele, with Professor Jacqueline Boyle as senior author, published in the Australian and New Zealand Journal of Public Health and announced by Monash University on 24 January 2025, tracked the trend between 2016 and 2021. That series uses a different data collection from the AIHW figure above and the two should not be laid end to end.

Within it, the largest increases were among mothers born in South-East Asia and in South and Central Asia. Rates among South-East Asian-born women rose from 12.2 per cent to 22.5 per cent, while among Australian-born women it went from 7.2 to 9.0; the release gives no percentage for South and Central Asia. It quotes the study’s finding that being born in all these regions of Asia is a risk factor because of genetic susceptibility, and that unfamiliarity with health services leaves migrant women with less opportunity to engage with preventive health practices.

That second point is the one a reader can do something about.

What this means at the appointment

If you are pregnant now, the question worth asking is what your service is doing about early screening, rather than which criteria would have applied to you last year. Ask at the booking visit whether an HbA1c is being ordered. Ask which criteria the pathology provider is using. If you had gestational diabetes in a previous pregnancy, say so at the first appointment rather than waiting for the form to ask.

If you were diagnosed under the old criteria and are now being told the threshold has moved, the diagnosis was not a mistake. The line was drawn in a different place, by people applying the evidence available to them, and the advice you were given about diet, monitoring and follow-up was the advice for the diagnosis you had.

On the years after the pregnancy the new paper is direct: women with gestational diabetes have an increased risk of future type 2 diabetes, kidney disease and cardiovascular disease. A diagnosis under either set of criteria is a reason to keep a GP in the picture long after the baby arrives.

Worth sitting with

A one in three rate in a community is a public health fact, not a verdict on any individual. The AIHW figure describes women born across an entire subcontinent and beyond, living here at every income and in every suburb. What the numbers do say is that the women this magazine writes for sit at the centre of the question the guideline set out to answer. A change made in a medical journal in June 2025 deserves to be explained at the antenatal clinic, in plain language, to the women it applies to most.