From the Guidelines
A normal menstrual cycle typically lasts 21-35 days, with menstruation (bleeding) occurring for 2-7 days, and is characterized by hormonal fluctuations that regulate ovulation and prepare the uterus for potential pregnancy. The cycle is divided into two main phases: the follicular phase, where estrogen levels rise as follicles develop in the ovary, culminating in ovulation around day 14 of a 28-day cycle, and the luteal phase, where progesterone increases to thicken the uterine lining 1. If pregnancy doesn't occur, hormone levels drop, triggering menstruation as the uterine lining sheds. Normal menstrual blood loss ranges from 30-80 mL, appearing bright to dark red. While some mild discomfort, breast tenderness, or mood changes may occur, severe pain or extremely heavy bleeding are not typical of a normal cycle. Regular cycles indicate proper hormonal function and reproductive health, though cycle length can vary between individuals and may change throughout a person's reproductive years.
Some key characteristics of a normal menstrual cycle include:
- Menstrual cycle length: 21-35 days
- Menstruation duration: 2-7 days
- Menstrual blood loss: 30-80 mL
- Hormonal fluctuations: estrogen and progesterone levels change throughout the cycle to regulate ovulation and prepare the uterus for potential pregnancy
- Ovulation: typically occurs around day 14 of a 28-day cycle
It's worth noting that irregular menstrual cycles, such as those with cycles less than 21 days or more than 35 days, can be a sign of an underlying gynecological problem, such as polycystic ovary syndrome (PCOS) or other hormonal imbalances 1. If irregular bleeding persists and is unacceptable to the woman, counseling on alternative contraceptive methods and offering another method if desired may be necessary 1. However, the most recent and highest quality study 1 provides the most relevant guidance on characterizing a normal menstrual cycle.
From the Research
Characteristics of a Normal Menstrual Cycle
- A normal menstrual cycle is characterized by high variability in cycle length, typically ranging from 26-35 days 2
- The cycle consists of three phases: follicular, ovulatory, and luteal, resulting in the formation of a mature follicle and release of an oocyte during each cycle 3
- Menses typically last for 3-7 days, with an average of 5.2 days 4
- Menstrual cycle regularity can vary, with 46% of women having a cycle range of 7 days or more, and 20% having a cycle range of 14 days or more 4
Hormonal Changes During the Menstrual Cycle
- The menstrual cycle is regulated by hormonal feedback loops, involving the hypothalamic-pituitary-ovarian axis 3
- Follicle-stimulating hormone (FSH) rises at the luteal-follicular transition, stimulating follicular growth and inhibin B secretion 2
- The ovulatory dominant follicle secretes oestradiol and inhibin A, while the corpus luteum secretes progesterone, oestradiol, and inhibin A in response to luteinizing hormone (LH) pulses 2
Clinical Implications
- Menstrual abnormalities, such as absence of menarche by age 15, absence of menses for three consecutive months, and menses lasting eight days or longer, warrant further evaluation 3
- Understanding normal menstrual patterns allows pediatric practitioners to provide appropriate counseling and education to adolescents and their families, and to identify menstrual abnormalities when they arise 3