uk-plab-1 MCQ (SBA): Ectopic pregnancy

A 29-year-old woman presents with 6 weeks of amenorrhoea, lower abdominal pain and light vaginal bleeding. She has a positive urinary pregnancy test. Transvaginal ultrasound shows no intrauterine pregnancy and a 2 cm adnexal mass. She is haemodynamically stable and her serum hCG is 1,500 IU/L and falling on serial measurements. What is the most appropriate management?