Managing gestational diabetes

Did you know gestational diabetes is the fastest-growing form of diabetes in Australia? Gestational diabetes (GDM) is commonly encountered in primary care during antenatal screening or preconception consultations and refers to hyperglycaemia first recognised during pregnancy.

Gestational diabetes risk factors and screening

Rates of GDM have risen significantly over the past 15 years, from 6.1% in 2011–12 to 19.3% in 2021–22, making it the fastest-growing form of diabetes in Australia. Poorly controlled GDM increases the risk of maternal and foetal complications, including macrosomia, shoulder dystocia, neonatal hypoglycaemia and future type 2 diabetes in both mother and child.

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All women should be screened for diabetes at their first antenatal appointment by considering risk factors such as previous GDM, polycystic ovarian syndrome (PCOS), obesity, and family history of diabetes. Certain medications (e.g. corticosteroids) and a history of adverse pregnancy outcomes, such as macrosomia or pregnancy-induced hypertension, also increase risk, along with multiparity and increasing maternal age.

Women with risk factors for GDM should be screened early in pregnancy. If an HbA1c has not been performed within the previous 12 months, HbA1c testing should be undertaken in the first trimester.

An oral glucose tolerance test (OGTT) is the gold standard for diagnosing GDM. An OGTT involves measuring fasting plasma glucose (FPG), followed by glucose measurements at 1 hour (1hPG) and 2 hours (2hPG) after ingestion of a 75g glucose drink. Women with previous GDM or early pregnancy HbA1c of 6.0–6.4% (42–47 mmol/mol) should undergo early OGTT before 20 weeks. All women should undergo an OGTT at 24–28 weeks, regardless of earlier screening results and risk factors.

GDM is diagnosed if one or more of the following thresholds are met during OGTT: (i) FPG ≥ 5.3–6.9 mmol/L; (ii) 1hPG ≥ 10.6 mmol/L; (iii) 2hPG ≥ 9.0–11.0 mmol/L. This can be further categorised as early GDM if the OGTT is performed before 20 weeks.

Of note, an HbA1c ≥ 6.5% (≥ 48 mmol/mol) in early pregnancy is diagnostic of overt diabetes in pregnancy (DIP) and likely indicates previously undiagnosed diabetes. Similarly, FPG ≥ 7.0 mmol/L, or a 2hPG ≥ 11.1 mmol/L at any time in pregnancy, indicates DIP. For women diagnosed with DIP, management is typically similar to that for women with pre-existing diabetes. Consideration should be given to the aetiology of diabetes, including autoimmune diabetes.

Gestational diabetes management

Pregnant women with GDM should be offered lifestyle advice and blood glucose monitoring. In most cases, GDM responds well to dietary and exercise modification, which can be trialled initially, with glucose-lowering therapies introduced if glycaemic targets are not achieved. Lifestyle advice focuses on appropriate weight gain, reducing high-glycaemic-index carbohydrates, and maintaining a balanced carbohydrate intake.

Self-monitoring of blood glucose is critical, usually four times daily (fasting and 1–2 hours after meals). Treatment targets typically include a fasting glucose of 4.4–5.5 mmol/L and a 2-hour postprandial glucose of 5.5–6.6 mmol/L. Pharmacological management is typically under the advice of secondary care, and insulin and metformin are the preferred agents.

In general practice, women should also be educated about their increased lifetime risk of developing type 2 diabetes. Women diagnosed with GDM should also undergo repeat OGTT at 6–12 weeks postpartum to assess for persistent glucose intolerance.

Gestational diabetes is increasingly common in pregnancy and requires early identification and management to reduce maternal and foetal risks. GPs play an important role in screening, patient education, and long-term follow-up to reduce future risk for both mother and child.

- Dr Samantha Miller, MBChB

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References

1. National Institute for Clinical Excellence (NICE). Treatment summaries: Diabetes, pregnancy and breast-feeding. https://bnf.nice.org.uk/treatment-summaries/diabetes-pregnancy-and-breast-feeding/
2. BMJ Best Practice (2025). Gestational Diabetes Mellitus. https://bestpractice.bmj.com/topics/en-gb/665
3. The Royal Australian College of General Practitioners (2018). Gestational diabetes mellitus: A pragmatic approach to diagnosis and management. https://www1.racgp.org.au/ajgp/2018/july/gestational-diabetes-mellitus
4. Department of Health, State Government of Victoria, Australia. Better Health Channel: Diabetes – Gestational. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/diabetes-gestational
5. Australian Institute of Health and Welfare (AIHW) (2024). Diabetes: Australian facts. https://www.aihw.gov.au/reports/diabetes/diabetes/contents/how-common-is-diabetes/gestational-diabetes
6. Diabetes UK (2026). Gestational Diabetes. https://www.diabetes.org.uk/about-diabetes/gestational-diabetes
7. Australasian Diabetes in Pregnancy Society (ADIPS). (2025). ADIPS 2025 consensus recommendations. Medical Journal of Australia. 223(3). https://www.mja.com.au/journal/2025/223/3/australasian-diabetes-pregnancy-society-adips-2025-consensus-recommendations