When a fertilized egg has been implanted in the lining of the uterus, the lining remains to nourish the fetus and is not discarded by menstruation. Oral contraceptives - Some women who take birth control pills may not have periods. When oral contraceptives are stopped, it may take the body 3 to 6 months to resume regular ovulation and menstruation. Breastfeeding - Mothers who breastfeed usually experience amenorrhea. Although ovulation may occur, menstruation may not.
Pregnancy can result even though menstruation is absent.
Stress - Mental stress can temporarily alter the functioning of the hypothalamus. Ovulation and menstruation may stop. Regular menstrual periods usually resume when stress is decreased. Medication - Certain medications can cause menstrual periods to stop. Illness - Chronic illness may postpone menstrual periods.