What is the normal duration of a menstrual cycle?

Menstrual Abnormalities and Normal Menstrual Cycle Duration

The normal menstrual cycle typically lasts between 21 and 35 days, with eumenorrhea defined as regular cycles occurring at intervals within this range. 1

Normal Menstrual Cycle Parameters

• Cycle length: 21-35 days in adult women 1
• Adolescent cycle length: 21-45 days 1
• Menses duration: Typically 5 days, but can vary 2
• Fertile phase: From 5 days before to the day of ovulation 2
• Ovulation: Generally occurs during days 9-20 in a standard 28-day cycle 1
• Cycle variation: Decreases with age, with the 5th-95th percentile range narrowing from 23-35 days in ages 15-19 to 23-30 days in ages 40-44 3

Common Menstrual Abnormalities

Cycle Length Abnormalities

• Polymenorrhea: Cycle length less than 21 days 3
• Oligomenorrhea: Cycles longer than 35 days 1, 3
• Amenorrhea:
  • Primary: No menarche by age 15 years 1
  • Secondary: Absence of three consecutive cycles or no menses for more than 45 days 1

Bleeding Pattern Abnormalities

• Hypomenorrhea: Abnormally light bleeding 1
• Menorrhagia/Hypermenorrhea: Abnormally heavy bleeding 1
• Metrorrhagia: Irregular bleeding between periods 4
• Premenstrual and postmenstrual spotting: Light bleeding before or after the main menstrual flow 1

Cycle Regularity Abnormalities

• Irregular cycles: Cycles varying by more than 14 days in length 3
• Subclinical menstrual defects: Abnormalities that may not be apparent without hormonal testing 1

Health Implications of Menstrual Abnormalities

• Metabolic implications: Menstrual irregularities are associated with metabolic syndrome, coronary heart disease, and type 2 diabetes 4
• Bone health: Estrogen deficiency from amenorrhea can lead to reduced bone density and increased risk of osteoporosis 5
• Fertility: Irregular cycles can indicate ovulatory dysfunction and potential fertility issues 4, 6
• Pregnancy outcomes: Irregular menstruation is associated with increased risk of pregnancy-related hypertensive disorders and adverse obstetric outcomes 4
• Quality of life: Menstrual disorders can significantly impact physical, mental, and social well-being 4

Relative Energy Deficiency in Sport (RED-S) and Menstrual Function

• Female Athlete Triad: The interrelationship between energy availability, bone health, and menstrual function 1
• Energy availability threshold: Energy availability below 30 kcal/kg fat-free mass per day is associated with menstrual disturbances 1
• Prevalence: Menstrual disorders affect up to 69% of dancers and collegiate long-distance runners 1
• Risk factors: Rapid weight loss, low body fat, high training volume, and psychological stress 1

Clinical Significance

• Menstrual cycle irregularities should be considered an important health indicator requiring evaluation 4, 5
• Regular monitoring of menstrual patterns throughout adolescence and adulthood can help identify potential health concerns early 5
• Evaluation of amenorrhea lasting more than 3 months is warranted, even in adolescents, as this exceeds the 95th percentile for cycle intervals 5
• Hormone monitoring technologies can provide more precise cycle tracking than relying on calendar-based estimates alone 6

Understanding normal menstrual cycle parameters and recognizing abnormalities is essential for early identification of potential health concerns and appropriate clinical intervention.