1. When a woman reaches menarche, the first period will start for her which can cause great variance in length. There can be 2 months without another period or periods can occur more frequently.
2. When the woman starts aging, they will get menopause and her cycles can be longer or shorter. A shortened cycle is very usual in this period and it is also a part of biological process.
3. The menopause can occur in some women before they reach 40 which are earlier than normal. Short menstrual cycles can also be a sign of ovarian dysfunction and those with this issue must go to a doctor.
4. A shortened cycle can be said as normal if it occurs once or twice a year. Sometimes the egg is not viable or a woman is under unexpected stress. The body of the woman can react by aborting a menstrual cycle to prepare for a time to bear children.