Normally, menstrual blood is dark red and non-clotting. If menstrual blood appears bright red, it is often associated with the following factors: First, submucosal fibroids or large interstitial fibroids can increase the endometrial area and affect the contraction of the uterus, which can cause menstrual blood to appear bright red and often accompanied by blood clots. Second, because of blood clotting disorders and thrombocytopenia can cause bright red menstrual blood. Thirdly, because of functional bleeding during puberty, clinically endocrine disorders and lowered estrogen can cause heavy vaginal bleeding, which is often bright red. In case of bright red menstrual blood, routine blood test, clotting time test, ultrasound test and sex hormone six test are recommended before giving treatment.