How do a period and implantation bleeding differ?

Big difference: Implantation bleeding doesn't really exist. If it does it is most likely ovulation or midcycle bleeding. This occurs during the middle of the month. Menstrual bleeding is the completion of a menstrual cycle, with shedding of the uterine lining, followed by your brain, ovaries and uterus starting the process all over again. (ie no pregnancy).