This case report highlights the prenatal diagnosis of a rare saccular inferior vena cava (IVC) aneurysm. A 25-year-old gravida 4 para 1 patient underwent detailed ultrasonography at 20 weeks of gestation, revealing a 15 x 10 x 14 mm infrarenal IVC aneurysm. Genetic analysis identified a de novo 2p16.3 deletion of uncertain significance. Serial imaging showed progressive aneurysm dilation and mild cardiomegaly. Postnatal CT angiography confirmed the aneurysm, and anticoagulant therapy was initiated. This report underscores the importance of detailed prenatal imaging and genetic evaluation in the identification and management of rare vascular anomalies, contributing to the understanding of their clinical implications.