"risky behavior"

First: I am not actively TTC but I have gotten pregnant before while on birth control, sadly that pregnancy ended in a miscarriage. Has anyone had an experience where they didn't know they were pregnant and continued doing things like drinking, etc.? If I ever had even a THOUGHT that I was pregnant I wouldn't do anything to harm the baby, but for me last time the only unusual symptom I had was being a week late on my period.