Urinoma is peripelvic extravasation of urine seen as the squeal of urinary trauma or stones. Little is known about maternal urinoma during pregnancy. A 27-year-old primigravida presented with gradual worsening right flank pain at 21(5/7) weeks of gestation. She denied any past medicosurgical history. Initial work-up revealed cost-vertebral angle tenderness and mild hydronephrosis by ultrasonography. Her symptom worsened and follow-up ultrasonography was performed 48 h later, which showed worsened hydronephrosis with large perinephric fluid collection. A Double-J stent was placed under cystoscopy. After the placement, the patient's symptoms improved quickly. The stent was removed three weeks later. The patient delivered vaginally at 39 weeks of gestation without complication. Maternal urinoma during pregnancy developed in the right side of the kidney in five of six reported cases (83.3%), and all were seen in the second half of pregnancy. All showed flank pain as the initial presentation. Ultrasonography for diagnosis was used in half of the patients. Fifty percent underwent Double-J stent before delivery and 16.7% after delivery. All cases delivered at term and 33.3% underwent cesarean delivery. Maternal urinoma is an important differential diagnosis for flank pain during pregnancy. Double-J stent placement was the main management. Close monitoring of the symptom with serial ultrasonography may be the key for diagnosis.