I would like to ask, how to distinguish between menstruation and abortion

Menstruation is a periodic change, generally 28 days to 30 days appear once, vaginal bleeding time will not exceed seven days, during which there may be dysmenorrhea and other symptoms, but after the end of menstruation symptoms will disappear. Abortion will appear vaginal bleeding and abdominal pain symptoms, bleeding volume is relatively large, if not treated in time, will not stop naturally, but also accompanied by uterine contractions and other symptoms.