Pathophysiology
Clinical meaning
The management of ectopic pregnancy requires a risk-stratified decision between medical therapy (methotrexate), surgical intervention (salpingostomy or salpingectomy), and expectant management. Methotrexate, a folic acid antagonist, works by inhibiting dihydrofolate reductase (DHFR), blocking thymidylate and purine synthesis, halting DNA replication in rapidly dividing trophoblast cells, and causing dissolution of the ectopic tissue over days to weeks. It is administered as a single-dose (50 mg/m² IM) or multi-dose protocol. Candidates for methotrexate must be hemodynamically stable with an unruptured ectopic, no fetal cardiac activity on ultrasound, beta-hCG ideally ≤5,000 mIU/mL (success rates decline above this threshold), and no contraindications (hepatic/renal impairment, immunodeficiency, blood dyscrasias, breastfeeding). Surgical management is indicated when methotrexate is contraindicated or has failed, when rupture has occurred or is imminent, or when the patient is hemodynamically unstable. Salpingostomy (linear incision on antimesenteric border of the tube to remove the ectopic pregnancy while preserving the tube) is preferred when the contralateral tube is damaged or absent and future fertility is desired; however, persistent trophoblast requiring subsequent methotrexate occurs in 5-20% of salpingostomy cases. Salpingectomy (complete tube removal) is definitive,...