uk-drcog MCQ (SBA): Ovarian Torsion Risk with Dermoid in Pregnancy

A 26-year-old woman at 34 weeks of gestation presents to the GP with sudden-onset right-sided abdominal pain. She has a history of a right ovarian dermoid cyst (4 cm) noted on booking ultrasound. She has nausea and vomiting. Her temperature is 37.0°C. Fetal movements are normal. Which is the single most important diagnosis to exclude?