A menstrual disorder is an irregular condition in a woman's menstrual cycle. Infrequent or irregular ovulation (usually defined as cycles of ≥36 days or <8 cycles a year) is called oligoovulation. Anovulation is absence of ovulation when it would be normally expected. Anovulation usually manifests itself as irregularity of menstrual periods, that is, unpredictable variability of intervals, duration, or bleeding. Anovulation can also cause cessation of periods or excessive bleeding.