Pregnancy. Inevitable abortion or miscarriage means you lost the baby with many causes such as blighted ovum, etc whereas ectopic pregnancy the egg is implanted in the fallopian tube, it is an emergency!
Need exam. Ectopic pregnancies can be mistaken for miscarriage easily. Both can cause cramps & bleeding, & pregnancy test is usually positive. The best way to tell them apart is to have a pelvic exam, often with an ultrasound.