ABSTRACTObjectiveTo assess the relationship between the cerebroplacental ratio (CPR) and intrapartum and perinatal outcomes in pregnancies complicated by gestational diabetes mellitus (GDM).MethodsThis was a retrospective cohort study of women with a non‐anomalous singleton pregnancy diagnosed with GDM who delivered at Mater Mothers' Hospital between 2007 and 2015. CPR was measured in 1089 cases between 34 + 0 and 36 + 6 weeks' gestation. CPR values were compared between groups categorized according to GDM treatment (by diet, oral hypoglycemic agent (OHA) or insulin). The association between CPR and intrapartum and perinatal outcomes was evaluated.ResultsNo difference in CPR was observed between treatment groups. Fetuses with CPR < 10th centile were significantly more likely to have adverse composite perinatal outcome (odds ratio (OR) = 2.93 (95% CI, 1.95–4.40)), preterm delivery and low birth weight than fetuses with CPR ≥ 10th centile (all P < 0.001). These associations were present regardless of the type of GDM treatment. Fetuses of women with insulin‐controlled GDM had poorer neonatal outcomes than did fetuses of women treated with OHA or dietary control alone. The risk of adverse outcome was significantly increased in the insulin‐treated group (OR = 1.75 (95% CI, 1.34–2.28); P < 0.001), which also had higher rates of preterm delivery and higher birth weight.ConclusionRegardless of the type of treatment, a low CPR is associated with poorer neonatal outcome in women with GDM. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.