I've seen women online say they have had heavy periods while being pregnant, how is this possible?

Internet is endless: It's possible if a woman is internet savvy and enjoys posting things. The internet is endlessly vast, and anyone can post anything on the internet. In real life, a woman cannot have a true menstrual period while she is pregnant (pregnancy stops the menstrual cycle). However, women can have vaginal bleeding during pregnancy, in which case they should contact their Ob-Gyn doctors for advice.

Its not: Its physiologically impossible to have a true period while you are pregnant. Some women have bleeding that looks like a period while they are pregnant but the mechanism is totally different and it is always worrisome for something serious like a miscarriage, and abruption, etc. Best wishes!