Background: The prevalence of type 2 diabetes mellitus (T2DM) and obesity in pregnancy is increasing in Australia. Contemporary local data are needed to quantify these risks and inform models of care.

Aim: To evaluate the association between T2DM and adverse maternal and neonatal outcomes among singleton births at Monash Health from 2016 to 2024.

Methods: A retrospective cohort study was conducted of singleton births >20 weeks gestation at a specialist maternity network in Australia during 2016-2024. Women with pre-existing T2DM were compared with women without diabetes; pregnancies affected by type 1 diabetes and gestational diabetes were excluded. Baseline characteristics were compared by T2DM status, and missing data was low for most variables. Multivariable logistic regression was used to examine associations between adverse maternal and neonatal outcomes, adjusting for maternal age, parity, body mass index (BMI), chronic hypertension, smoking, polycystic ovarian syndrome (PCOS), socioeconomic status and ethnicity. Median HbA1C association with outcomes will be assessed. A subgroup analysis (2023-2024) will explore metformin exposure in relation to gestational weight gain, glycaemic control and perinatal outcomes.

Results: 61,996 singleton pregnancies were included, comprising 757 women with T2DM and 61,239 women without diabetes. Compared to women without diabetes, women with T2DM were older (34.12±4.91 vs 30.47±5.17 years), had higher parity (1.49±1.54 vs 0.98±1.16), and markedly higher preconception BMI (31.84±7.77 vs 25.83±6.04 kg/m²). In adjusted analyses, T2DM was associated with higher odds of preeclampsia (aOR 2.46, 95% CI 1.89–3.21), elective or emergency caesarean section (aOR 1.88, 95% CI 1.62–2.19), preterm birth <37 weeks (aOR 2.11, 95% CI 1.73–2.57), large for gestational age (aOR 2.46, 95% CI 2.07–2.92), macrosomia (aOR 1.33, 95% CI 1.09–1.61), NICU/SCN admission (aOR 3.28, 95% CI 2.55–4.21), and neonatal hypoglycaemia (aOR 2.88, 95% CI 2.36–3.53). No significant associations were observed for perineal trauma, prolonged labour, small for gestational age, congenital anomalies or perinatal mortality.

Conclusion: T2DM was associated with substantially increased risks of major maternal and neonatal complications. These findings reinforce the need for intensified, multidisciplinary antenatal care and highlight opportunities to refine risk stratification and optimise pre‑pregnancy and early‑pregnancy management for women with T2DM.