Is menstrual cycle 20 days normal?

Normal menstrual cycle frequency should be between 21-35 days, less than 21 days of menstrual cycle is frequent menstruation. If occasionally or after the application of drugs show menstrual cycle shortening, generally do not need to worry, but if the menstrual cycle is always maintained in 20 days, it is necessary to according to the specific condition and symptoms, the corresponding examination, eliminate organic diseases caused by menstrual cycle shortening, timely adjustment of endocrine function. Each person's menstruation is slightly different, check if there is no abnormality, as long as the menstruation can be timely clean, do not worry about it.