A systematic review examines the association between maternal vitamin D deficiency and fetal growth restriction (FGR) or small for gestational age (SGA), which contribute to perinatal morbidity and mortality. Vitamin D deficiency impairs placental development and fetal growth through angiogenesis, immune regulation, and oxidative stress. From the 48 included studies, there is a consistent association of low maternal 25(OH)D concentrations with an increased risk of FGR and SGA, including dose dependence at lower thresholds. Associations with preterm birth were similar but less consistent. Results of intervention studies on vitamin D supplementation were heterogeneous due to differences in dosage, timing, baseline vitamin D status, and adherence. Experimental studies confirm biological plausibility through effects on placental angiogenesis, immunity, endocrine signaling and oxidative stress. Standardized doses, harmonized diagnostic thresholds and better controlled interventions are needed to prevent FGR and SGA. The overview is registered under CRD42024622395.