What is the duration and phases of a normal menstrual cycle?

Normal Menstrual Cycle Duration and Phases

The normal menstrual cycle typically lasts between 21 and 35 days in adult women, with distinct follicular, ovulatory, and luteal phases that regulate reproductive function and overall health. 1

Normal Cycle Parameters

• The normal menstrual cycle ranges from 21-35 days in adult women, with adolescents having a wider normal range of 21-45 days 1
• Menstruation (menses) typically lasts 3-7 days with an average blood loss of 30-80 mL 2
• A cycle is counted from the first day of bleeding (day 1) to the day before the next menstrual period begins 3
• Eumenorrhea refers to regular menstrual cycles occurring at intervals within the normal range 1

Phases of the Menstrual Cycle

Follicular Phase

• Begins on day 1 of menstruation and continues until ovulation 3
• Variable length (typically 7-21 days), accounting for most of the variation in overall cycle length 3
• Characterized by FSH rise at the luteal-follicular transition, stimulating follicular growth 3
• Early follicular phase features cohort follicle development and inhibin B secretion 3
• Mid-follicular phase involves dominant follicle selection 3
• Late follicular phase shows increasing estradiol and inhibin A secretion from the dominant follicle 3

Ovulatory Phase

• Occurs during days 9-20 in a standard 28-day cycle 1
• Triggered by LH surge in response to rising estradiol levels 3
• Results in release of mature oocyte from dominant follicle 2
• The fertile window extends from 5 days before to the day of ovulation 3

Luteal Phase

• Begins after ovulation and lasts until the start of the next menstrual period 3
• More consistent length (typically 12-14 days) 3
• Characterized by corpus luteum formation, which secretes progesterone, estradiol, and inhibin A 3
• Corpus luteum reaches peak size, secretion, and vascularization 6-7 days after ovulation 3
• In the absence of pregnancy, the corpus luteum regresses, leading to declining hormone levels and menstruation 3

Follicle Wave Patterns

• Two-thirds of women show two follicle waves per cycle, while one-third show three follicle waves 3
• Women with three follicle waves typically have longer cycles, later estradiol rise, and later LH surge 3

Age-Related Changes

• Follicular phase length tends to decline with age, while luteal phase length increases 4
• Cycle variability is greater during adolescence and perimenopause 2

Clinical Significance

• The menstrual cycle serves as a vital sign and important indicator of overall health in women 2, 5
• Irregular menstruation (cycles <21 or >35 days) may signal underlying health concerns 6
• Absence of menses for three consecutive months warrants evaluation 2
• Regular menstrual cycles are associated with proper bone health and prevention of osteoporosis 5

Common Pitfalls in Assessment

• Assuming all women have 28-day cycles with equal follicular and luteal phases 4
• Overlooking menstrual irregularities as normal variants in adolescents 5
• Failing to recognize that cycle length and phase duration vary significantly between individuals 3
• Not considering that hormone patterns throughout the cycle provide crucial information about reproductive health 4