There are the following clinical differences between bleeding from pregnancy and bleeding from menstruation: First, bleeding from pregnancy will have clots. Pregnancy is in a hypercoagulable state, so there will be clots, while menstrual blood is non-coagulable, so there are often no clots in menstrual blood when menstruation occurs. Secondly, the vast majority of bleeding caused by pregnancy is clinically fresh, while menstrual blood is dark red. Third, vaginal bleeding due to pregnancy is accompanied by corresponding gastrointestinal reactions, such as nausea and vomiting, while vaginal bleeding due to menstruation does not occur clinically with nausea and vomiting. Unless there is a history of severe dysmenorrhea in the clinical setting and a history of dysmenorrhea in the past, this is the main clinical difference between the two. Also, blood HCG is negative when you have a period and positive when you bleed from pregnancy.