In 2020–21, around 1 in every 6 women who gave birth in hospital were diagnosed with gestational diabetes (49,000 women).
The following factors increase a woman’s risk of developing gestational diabetes:
- ethnicity: Asian, Indian subcontinent, Aboriginal, Torres Strait Islander, Pacific Islander, Māori, Middle Eastern, non-white African
- pre-pregnancy body mass index (BMI) >30 kg/m²
- previous hyperglycaemia in pregnancy
- previous elevated blood glucose level
- maternal age ≥40 years
- family history of diabetes mellitus (close relative with diabetes or a sister with hyperglycaemia in pregnancy)
- previous macrosomia (baby with birth weight >4500g or >90th percentile)
- polycystic ovary syndrome
- medications: corticosteroids, antipsychotics (Nankervis et al. 2014).
Diagnostic criteria
The Australasian Diabetes in Pregnancy Society guidelines recommend the 75g oral glucose tolerance test (OGTT) for all pregnant women at 24–28 weeks’ gestation and re-testing with the 75g OGTT at 6–12 weeks’ post-partum for women diagnosed with gestational diabetes (identifying ongoing glucose issues which may indicate other forms of diabetes first detected in pregnancy). Regular, ongoing monitoring is also recommended due to the high risk of recurrence in subsequent pregnancies and of developing type 2 diabetes in the future.
A diagnosis for gestational diabetes (using the International Association of Diabetes and Pregnancy Study Groups criteria) is made based on the 75g OGTT with one or more of the following values:
- fasting plasma glucose ≥5.1mmol/L
- 1-hour post 75g oral glucose load ≥10.0 mmol/L
- 2-hour post 75g oral glucose load ≥8.5 mmol/L (Nankervis et al. 2014).
In 2020–21, just over 49,000 women aged 15–49 who gave birth in an Australian hospital were diagnosed with gestational diabetes (16.3%).
Variation by age
The incidence of gestational diabetes increases linearly with age, ranging from 7.8% to 31.3% in the 15–19 and 45–49 age groups, respectively in 2020–21. Compared with women aged 15–19, those aged 35–39 were 2.6 times as likely to be diagnosed with gestational diabetes while women aged 40–44 and 45–49 were 3.3 and 4.0 times as likely, respectively (Figure 1).