INTRODUCTION: Our objective was to evaluate the strength of association and diagnostic performance of cerebroplacental ratio (CPR) in predicting the outcome of pregnancies complicated by pre- and gestational diabetes mellitus. METHODS: PubMed, Embase, Cochrane, and Google Scholar databases were searched. Inclusion criteria were pregnancies complicated by gestational or pregestational diabetes undergoing ultrasound assessment of CPR. The primary outcome was a composite score of perinatal mortality and morbidity as defined by the original publication. The secondary outcomes included preterm birth gestational age (GA) at birth, mode of delivery, fetal growth restriction (FGR) or small for GA (SGA) newborn, neonatal birthweight, perinatal death (PND), Apgar score <7 at 5 min, abnormal acid-base status, neonatal hypoglycemia, admission to neonatal intensive care unit (NICU). Furthermore, we aimed to perform a number of sub-group analyses according to the type of diabetes (gestational and pregestational), management adopted (diet insulin or oral hypoglycemic agents), metabolic control (controlled vs. non-controlled diabetes), and fetal weight (FGR, normally grown, and large for GA fetuses). Head-to-head meta-analyses were used to directly compare the risk of each of the explored outcomes. For those outcomes found to be significant, computation of diagnostic performance of CPR was assessed using bivariate model. RESULTS: Six studies (2,743 pregnancies) were included. The association between low CPR and adverse composite perinatal outcome was not statistically significant (p = 0.096). This result did not change when stratifying the analysis using CPR cut-off below 10th (p = 0.079) and 5th (p = 0.545) centiles. In pregnancies complicated by GDM, fetuses with a low CPR had a significantly higher risk of birthweight <10th percentile (OR: 5.83, 95% confidence interval [CI] 1.98-17.12) and this association remains significant when using a CPR <10th centile (p < 0.001). Fetuses with low CPR had also a significantly higher risk of PND (OR: 6.15, 95% CI 1.01-37.23, p < 0.001) and admission to NICU (OR 3.32, 95% CI 2.21-4.49, p < 0.001), but not of respiratory distress syndrome (p = 0.752), Apgar score <7 at 5 min (p = 0.920), abnormal acid-base status (p = 0.522), or neonatal hypoglycemia (p = 0.005). These results were confirmed when stratifying the analysis including only studies with CPR <10th centile as a cut-off to define abnormal CPR. However, CPR showed a low diagnostic accuracy for detecting perinatal outcomes. CONCLUSION: CPR is associated but not predictive of adverse perinatal outcome in pregnancies complicated by gestational diabetes. The findings from this systematic review do not support the use of CPR as a universal screening for pregnancy complication in women with diabetes.