Menstrual synchrony by chance when there is menstrual cycle variability. Yang and Schank argued that when there is cycle variability (i.e., either women have irregular cycles, have cycles of different frequencies, or both), most women will have the opportunity to experience synchrony even though it is a result of cycle variability and not a result of a mechanism such as the exchange of pheromones. For example, consider two women A and B. Suppose A has menstrual cycles that are 28 days long and B has cycles that are 30 days long. Suppose further that when A and B become close friends, B
Menstrual disorder Menstrual disorder A menstrual disorder is an abnormal condition in a woman's menstrual cycle. Disorders of ovulation include oligoovulation and anovulation: "Polymenorrhea" is the medical term for cycles with intervals of 21 days or fewer. "Irregular menstruation" is where there is variation in menstrual cycle length of more than approximately eight days for a woman. The term "metrorrhagia" is often used for irregular menstruation that occurs between the expected menstrual periods. "Oligomenorrhea" is the medical term for infrequent, often light menstrual periods (intervals exceeding 35 days). "Amenorrhea" is the absence of a menstrual period in a woman of reproductive age.