Test not useful in case of tubal pregnancy:
High-Yield Explanation
HSG is usually done within 10 days of the period and after cessation of flow.This is inorder to reduce retrograde flow of the menstrual endometrium,which can result in infection and endometriosis.During menstruation the uterine veins are much dilated and this can cause increased vascular intravasation (refer pgno:125 sheila gynaec 2 nd edition)