Under normal circumstances, menstruation occurs once a month. However, some people have a long ovarian secretion cycle and will have a period once every two months. As long as there is regularity, medically a period once every two months is called a concurrent period, a period once every three months is called a residence period, and some people will have a period once every six months. The effect of ovarian function is not a big problem as long as there is regularity. Therefore, under normal circumstances, most women have menstruation once a month, and a very small number of people have menstruation once a month, as long as there is regularity, and as long as the body functions are not problematic, it is normal. So, generally, menstruation is not regular, the length of time to come is different to be abnormal. These cases are normal menstruation, if not these cases, menstruation is not regular, then it is abnormal.