Introduction: Women with gestational diabetes mellitus (GDM) are more likely to have adverse maternal and neonatal outcomes. From January 2015, Queensland Health adopted new diagnostic criteria for GDM following the results of the HAPO trial. We aimed to determine whether the introduction of the new criteria has resulted in improved perinatal outcomes.

Methods: We conducted a retrospective matched case control study over 4 years at a tertiary obstetric hospital. Patients diagnosed with GDM by the pre‐2015 criteria were compared to patients diagnosed with the updated criteria. Cases were matched by maternal age, BMI and nulliparity to controls in a 1:1 ratio. Outcomes assessed included incidence of GDM as well as neonatal outcomes. Demographic and outcome data were analysed with t‐test and chi‐squared tests.

Results: There were 3869 women in each group. There was no difference in demographic data for maternal age (p = 0.458), nulliparity (p = 0.588), or BMI (p = 0.814). Updated criteria led to an increase in women with dietary controlled GDM (7.0% vs 4.7%, p < 0.001) and GDM requiring insulin (4.2% vs 3.2%, p < 0.001), and was associated with more frequent nursery admissions (2.3% vs 1.9%, p = 0.023). There was no difference in birthweight (p = 0.256), gestational age at delivery (p = 0.348), Apgar<7 at 5 mins (p = 0.301), mode of birth (p = 0.135) or shoulder dystocia (p = 0.752).

Conclusion: The new diagnostic criteria has led to an increase in the diagnosis of GDM and subsequently an increase in service burden. This has not demonstrated any improvements in perinatal outcomes, and rather, special care nursery admissions were increased.