The right subclavian artery (RSA) — superior vena cava (SVC) fistula is a rare form of arteriovenous fistula, characterized by the presence of abnormal channels connecting arteries and veins. For the first time, we report the diagnosis of an RSA-SVC fistula in a fetus. It can be challenging to differentiate this condition from supra-cardiac total anomalous pulmonary venous connection (TAPVC). However, findings suggest that simultaneous dilation of the innominate artery and superior vena cava, bidirectional blood flow within the aortic arch, and a biphasic unidirectional spiculated blood flow spectrum at the confluence can serve as three key indicators for differentiation.