Colonic obstruction due to sigmoid colon volvulus during pregnancy is a rare but complication with significant maternal and fetal mortality. That requires prompt surgical intervention (decompression) to avoid intestinal ischemia and perforation. We report the case of a 38-week pregnant woman with abdominal pain and subsequent development of constipation. Preoperative diagnosis was achieved using ultrasonography: the large bowel distension and a typical whirl sign - near a sigmoid colon transition point - suggested the diagnosis of sigmoid volvulus. The decision to refer the patient for emergency laparotomy was adopted without any ionizing radiation exposure, and the pre-operative diagnosis was confirmed after surgery. Sigmoid volvulus complicating pregnancy is a rare, non-obstetric cause of abdominal pain.