Evidence on long‐term trends in gestational diabetes mellitus (GDM) prevalence in Australia is lacking.

To assess and compare trends in GDM prevalence among Indigenous and non‐Indigenous Australian women.

Materials and Methods
Analysis of crude and age‐adjusted GDM prevalence over time by Indigenous status and age, using routinely collected midwives data from Australian states and territories on mothers giving birth from 1990 to 2009.

Despite considerable data variation, particularly in 1990–1999, and likely underestimation of GDM prevalence, crude and age‐adjusted GDM prevalences were higher in Indigenous than non‐Indigenous women at all time‐points (4.7% vs 3.1% in 1990–1999; 5.1% vs 4.5% in 2000–2009, P < 0.0001). Data variability precluded quantitative assessment of trends and changes in prevalence ratios before 2000. From 2000 to 2009, GDM prevalence increased significantly among Indigenous women by a mean 2.6% annually (Ptrend<0.0001), and non‐Indigenous women by 3.2% annually (Ptrend<0.0001), with no significant trend in the age‐adjusted Indigenous/non‐Indigenous prevalence ratios (PR) (P = 0.34). GDM prevalence increased significantly with age (P < 0.0001), although the increase with age was significantly greater among Indigenous women (PR 5.34 (4.94–5.77), ≥35 vs <25 years) compared to non‐Indigenous women (PR 3.72 (3.64–3.81), ≥35 vs <25 years), Pinteraction<0.0001. Conclusions Bearing data quality concerns in mind, GDM prevalence is increasing rapidly among Australian women, more than doubling in non‐Indigenous women between 1990 and 2009. Prevalence is consistently higher in Indigenous versus non‐Indigenous women, with statistically consistent differences between the groups in recent years. The marked increase in prevalence with age highlights an important period for prevention, particularly for Indigenous women.