A 26-year-old pregnant woman visits her gynecologist for a routine checkup. Ultrasound examination reveals that the patient has a normal pregnancy but that she also has two uteri. What is the most likely embryologic explanation of this condition?

A double uterus is caused by failure of inferior parts of the paramesonephric ducts. A complete fusion results in abnormal development of the uterine tubes because the uterine tubes form from the unfused portions of the cranial parts of the paramesonephric ducts. Hydronephros, swelling of the renal pelvis and calyces with urine, can result from the obstruction of the ureter by a renal stone. Cryptorchidism is a condition characterized by an undescended testis, in which the testis can be localized in the abdominal cavity or in any place along the path of testicular descent. The pronephros is part of the primordial urinary system and generally degenerates in the first four weeks of development.