A 23 year old woman presents with intermittent pain in the left lower abdomen for 3 days. The pain was dull at first, but became sharp and colicky last night, with radiation to the left thigh and associated nausea and vomiting.

Her medical, surgical and family histories are unremarkable. She is sexually active and is on combined oral contraceptive pills. Her last withdrawal bleed was 21 days ago.

She does not smoke, only drinks socially, and denies recreational drug abuse.