Aim: To investigate whether ductus venosus (DV) wave velocities and/or DV peak velocity index for veins (DV-PVIV) can predict failure of functional closure of the foramen ovale in the postnatal period. Material and methods: Fetal echocardiography was performed in 455 healthy women with uneventful pregnancies between the 20-24th gestational weeks. DV blood flow and DV-PVIV data were collected prospectively. Echocardiography was repeated in healthy subjects on the 30th postnatal day. Four hundred patients met the study criteria. Newborns with clearly visible foraminal flaps, interatrial septal defects smaller than 5 mm and right-to-left shunting through the defect were accepted as patent foramen ovale (PFO) (n=91). Newborns without PFO (n=309) comprised the control group. Results: A statistically significant difference was detected between the groups with and without PFO in terms of mean DV-PVIV values, DV-D and DV-a wave velocities (p<0.05 for all). ROC analysis showed that increased DV-PVIV values were related to and predictive of PFO (AUC=0.75; p<0.001) and that a threshold value of 0.62, had a sensitivity of 86.8% (95% CI 78.1-93.0%) and a specificity of 51.7% (95% CI 46.1-57.5%). Conclusion: DV-PVIV values above 0.62 at the time of fetal echocardiographic examination can predict failure of functional closure of the foramen ovale in the postnatal period.