Periods with no abdominal pain and no blood clots are usually normal. A moderate amount of menstruation, dark red in color, with a small amount of blood clots or no blood clots is normal. During menstruation prostaglandins promote uterine contractions, and uterine smooth muscle, if over-contracted, can lead to ischemia and hypoxia of the smooth muscle, resulting in abdominal pain; if the response to prostaglandins is not very sensitive or if the uterus is contracting normally, and is not over-contracted, then it may not cause pain. Normal menstrual period is 2-8 days, if it is significantly shorter with low or prolonged volume, it is abnormal. Normal menstrual flow is between 20 and 60 ml, but more than 80 ml or less than 5 ml is abnormal. If you have these symptoms, you should consult a doctor who can identify the cause and give you targeted treatment.