How many weeks can an ectopic pregnancy be detected?

Suspected. Ectopic can sometimes be suspected by 4 weeks ega (or before) based on blood levels. At 4 weeks (2 weeks after the missed expected menstrual period) it's still unlikely to positively identify ectopic on ultrasound. It's often difficult or impossible to make a 100% certain diagnosis until 5, 6, or later weeks ega; but ectopic can be strongly suspected before then.