The objective of this study is to identify fetal echocardiographic measures that predict postnatal coarctation of the aorta (CoA). A retrospective review of patients from 2013 to 2017 identified 13 cases of prenatal diagnosis of CoA confirmed postnatally and 14 cases of prenatal diagnosis of CoA with normal arches postnatally. There were 30 controls. Measurements were made and indices applied on all available longitudinal fetal echocardiograms for each patient. Linear mixed effects models were used to examine the between-group differences in the trajectories of the measurements. Significant differences were seen in the true CoA group for the following: smaller distal transverse arch diameter to distance between the left common carotid and left subclavian arteries (DT/LCA–LSCA) index (p = 0.04), smaller distal transverse arch diameter (p = 0.005), and longer brachiocephalic to left common carotid artery (LCA) (p = 0.004) and LCA–left subclavian artery (LSCA) distances (p < 0.0001). Additionally, the LCA/DT index trend appears to differentiate false positives from true coarctations (p < 0.03). The fetal echocardiographic DT/LCA–LSCA index, brachiocephalic–LCA distance and LCA–LSCA distance are significant predictors of postnatal coarctation. The LCA/DT index trend over time may differentiate which of those patients with prenatal concern for coarctation are more likely to develop coarctation postnatally. The use of fetal echocardiographic measures may improve prenatal detection and predication of postnatal coarctation.