Menstrual cycle: cyclical reproductive change recurring about monthly in women, externally marked by periodic vaginal bleeding (menstruation); divided into follicular and luteal phases separated by ovulation.
Normal length: 28 days (range 21 to 35 days); each phase lasts 14 days in a 28-day cycle, and luteal phase length is constant regardless of cycle length.
Ovarian and Endometrial Changes Across the Cycle
Cycle length is frequently influenced by psychological, environmental, nutritional and social factors; the cycle physiologically ceases during pregnancy and lactation.