What is the normal timing of menstrual cycles?

From the Guidelines

A normal menstrual cycle typically lasts between 21 to 35 days. The cycle is measured from the first day of one period to the first day of the next period 1. Menstruation itself usually lasts 3 to 7 days, with most women experiencing a flow for about 5 days. The amount of blood lost during a normal period ranges from 30 to 80 milliliters.

Key Points to Consider

• Cycle length can vary from woman to woman and even from cycle to cycle in the same woman.
• Variations in cycle length are particularly common during the first few years after menarche (first period) and in the years approaching menopause.
• These variations occur because of hormonal fluctuations that affect ovulation timing, as noted in the context of ovarian dysfunction and POI surveillance 1.
• The menstrual cycle is regulated by hormones including estrogen and progesterone, which rise and fall throughout the cycle to control the thickening of the uterine lining and its shedding during menstruation.
• If your cycles consistently fall outside the normal range (shorter than 21 days or longer than 35 days), are extremely painful, or involve very heavy bleeding, it would be advisable to consult with a healthcare provider as these could indicate underlying health issues.

Factors Influencing Menstrual Cycle Timing

• Hormonal changes: Fluctuations in estrogen and progesterone levels can affect cycle length and regularity.
• Age: Menstrual cycles can be irregular during the first few years after menarche and in the years leading up to menopause.
• Health conditions: Certain medical conditions, such as polycystic ovary syndrome (PCOS), can impact menstrual cycle regularity.
• Lifestyle factors: Stress, weight changes, and certain medications can also influence menstrual cycle timing. Given the information from the study 1, it's essential to understand that while the study focuses on premature ovarian insufficiency surveillance, the definition of irregular menstrual cycles as those less than 21 days or more than 35 days provides a benchmark for what is considered a normal menstrual cycle duration.

From the Research

Normal Menstrual Cycles Timing

The timing of normal menstrual cycles can vary from person to person, but research suggests that hormonal contraceptives can help regulate menstrual cycles.

• A study published in 2022 2 found that metformin, GLP-1-analogues, and supplements were effective in regulating menstrual cycles in adolescents diagnosed with PCOS.
• Another study published in 2024 3 investigated the effects of contraceptive techniques, such as contraceptive pills and long-acting reversible contraceptives, on menstrual morbidity and found that hormonal contraceptives can be used to treat adverse conditions associated with menstruation.
• A review published in 2023 4 examined the impact of menstrual cycle hormones and oral contraceptives on key aspects of female physiology and found that the differences between the follicular and luteal phases and between OC active and placebo phases are relatively subtle.

Factors Affecting Menstrual Cycle Timing

Several factors can affect menstrual cycle timing, including:

• Hormonal changes: Fluctuations in estrogen and progesterone levels can impact menstrual cycle timing 4.
• Contraceptive use: Hormonal contraceptives can help regulate menstrual cycles, but may also have varying effects on different individuals 3.
• PCOS: Polycystic ovary syndrome (PCOS) can cause menstrual irregularities, and treatment options such as metformin and supplements may be effective in regulating menstrual cycles 2.