Maternal diabetes, fetal growth and stillbirth risk: A population-wide retrospective cohort study from Victoria, Australia

Objective: To determine the relationships between diabetes in pregnancy, birthweight and stillbirth risk using population-based data. Research Design and Methods: All singleton births in Victoria, Australia between 2009–2020 were linked with perinatal and diabetes data. For each diabetes subgroup (type 1, type 2 and gestational diabetes (diet-controlled, insulin-controlled)), we assessed the proportion of infants with a birthweight <10th or >97th centile, the probability of stillbirth by birthweight centile, and stillbirth rate per 1,000 pregnancies across gestational age. Results: Our study cohort of 860,042 included 100,856 pregnancies (11.7%) complicated by diabetes in pregnancy. Compared with no diabetes, women with diabetes in pregnancy gave birth earlier (median 38.7 weeks’ gestation vs. 39.4) and had more iatrogenic births (65% vs. 44%). Gestational diabetes was associated with a lower overall risk of stillbirth compared with no diabetes (diet-controlled: relative risk [RR] 0.75 [95%CI: 0.64–0.89], insulin-controlled: RR 0.37 [95%CI: 0.25–0.53]). Compared with no diabetes, pre-existing diabetes was associated with an increased risk of stillbirth (RR 2.68 [95%CI: 2.01–3.56]), with this trend persisting across all gestational ages and birthweights. This was particularly observed among infants >97th centile (type 1 diabetes: RR 3.96 [95%CI: 1.23–12.76]; type 2: RR 4.02 [95%CI: 1.71–9.47]). Conclusions: In our cohort, gestational diabetes was associated with a lower stillbirth risk compared with no diabetes, potentially explained by increased monitoring and earlier iatrogenic delivery. Pre-existing diabetes was associated with a higher overall risk of stillbirth, with macrosomic fetuses >97th centile representing a particularly high-risk group, requiring close monitoring.