The best way to definitely diagnose an ectopic pregnancy is ?
The usual and regular way to diagnose an ectopic is the Transvaginal USG Serial bHCG levels are helpful adjuncts and not superior to TVS MRI is the best imaging technique to diagnose an ectopic and is considered a 'Trouble Shooter' when there is a doubt. Best method to diagnose an ectopic pregnancy irrevocably is Laparoscopy
Laparoscopy
Culdocentesis
serial bHCG levels and correlate with doubling titres
USG
Ectopic Pregnancy (Hello ! Where are you ?)