Menstrual cycle shortest and longest cycle lengths is considered very irregular. The average menstrual cycle lasts 28 days. The variability of menstrual cycle lengths is highest for women under 25 years of age and is lowest, that is, most regular, for ages 25 to 39. Subsequently, the variability increases slightly for women aged 40 to 44. The luteal phase of the menstrual cycle is about the same length in most individuals (mean 14.13 days, standard deviation 1.41 days) whereas the follicular phase tends to show much more variability (log-normally distributed with 95% of individuals having follicular phases between 10.3 and 16.3 days).
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.