Maternal Diabetes, Fetal Growth and Stillbirth Risk: A Population-Wide Retrospective Cohort Study From Victoria, Australia

Abstract

OBJECTIVE To determine the relationships between diabetes in pregnancy, birth weight, and stillbirth risk, using population-based data. RESEARCH DESIGN AND METHODS All singleton births in Victoria, Australia, between 2009 and 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 birth weight in <10th or >97th centile, the probability of stillbirth by birth weight 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 gestation 38.7 weeks 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 0.25–0.50]). Compared with no diabetes, preexisting 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 birth weights. This was particularly observed among infants in the >97th centile (type 1 diabetes: RR 3.96 [95% CI 1.23–12.76]; type 2 diabetes: 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, which potentially can be explained by increased monitoring and earlier iatrogenic delivery. Preexisting diabetes was associated with a higher overall risk of stillbirth, with macrosomic fetuses in the >97th centile representing a particularly high-risk group requiring close monitoring.