In clinical practice, the majority of women have a menstrual cycle of 28-30 days, but some have different menstrual cycles due to individual differences. Some may have a menstrual cycle of 35 or 38 days, which is normal, while others have a quarterly menstrual cycle, also known as quarterly menstruation. It is advisable for such women to have a blood test for sex hormones on the second or third day of menstruation to find out if the endocrine system is normal, and then to find out if ovulation is normal.