Black period blood and vaginal discharge may look frightening, but it isn’t a cause of concern at all times. You may notice black coloured vaginal discharge throughout your menstrual cycle, particularly at the beginning of your periods. Black period blood is blood that takes more time to leave your uterus and gets oxidized in the process. This may make this blood darker in colour. Hence, it appears as a dark brown or black period blood. This blood often has as a resemblance to coffee grounds. However, in some cases, you should see your doctor for black coloured vaginal discharge. So if you're sure, please see your doctor as soon as possible.