Understanding the Menstrual Cycle

What Is the Menstrual Cycle?

The menstrual cycle is the monthly process by which the body prepares for a possible pregnancy. It is counted from the first day of one period to the first day of the next.

• Average cycle length: 28 days, but anywhere from 21 to 35 days is considered normal for adults (Cleveland Clinic, NHS).
• Average period length: 3–7 days.
• Cycles can vary in length from month to month, especially during adolescence and approaching menopause.

The Four Phases

1. Menstruation (Day 1–5 approximately)

The uterine lining sheds, resulting in bleeding. This is "your period." Hormone levels (oestrogen and progesterone) are at their lowest.

2. Follicular Phase (Day 1–13 approximately)

Overlaps with menstruation. The pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the ovaries to develop follicles. One follicle becomes dominant. Oestrogen rises, causing the uterine lining to thicken.

3. Ovulation (Around Day 14)

A surge of luteinising hormone (LH) triggers the release of a mature egg from the ovary. This is the most fertile point of the cycle. The egg survives for about 12–24 hours after release.

4. Luteal Phase (Day 15–28 approximately)

The empty follicle becomes the corpus luteum and produces progesterone, which maintains the uterine lining. If the egg is not fertilised, progesterone drops, and the lining begins to shed — starting the next cycle.

Understanding Ovulation

Ovulation is the release of an egg from the ovary. Key points:

• It typically occurs about 14 days before the next period (not necessarily 14 days after the last one).
• Signs of ovulation may include mild lower abdominal pain, changes in cervical mucus (becoming clear and stretchy), and a slight rise in basal body temperature.
• Ovulation can be irregular, especially during stress, illness, or hormonal changes.

The Fertile Window

The fertile window is the time during which pregnancy is possible:

• Approximately 5 days before ovulation and the day of ovulation itself.
• Sperm can survive in the reproductive tract for up to 5 days.
• The egg is viable for about 12–24 hours after release.

Understanding the fertile window is relevant both for those trying to conceive and those trying to avoid pregnancy.

Why Cycles Differ

Many factors affect cycle length and regularity:

• Age — Cycles are often irregular in the first few years after menarche (first period) and in the years approaching menopause.
• Stress — Physical or emotional stress can delay ovulation and alter cycle length.
• Weight changes — Significant weight gain or loss can affect hormones and cycle regularity.
• Exercise — Very intense exercise can cause irregular or absent periods.
• Medical conditions — Polycystic ovary syndrome (PCOS), thyroid disorders, and other conditions can affect cycles.
• Contraception — Hormonal contraception can change or stop periods.

Myths vs Facts

Myth: A normal cycle is always 28 days. Fact: Cycles between 21 and 35 days are considered normal for adults.

Myth: You cannot get pregnant during your period. Fact: While less likely, pregnancy is possible if you have a shorter cycle and ovulate early.

Myth: Irregular periods always mean something is wrong. Fact: Occasional irregularity is common, especially during adolescence, after pregnancy, or approaching menopause. Persistent irregularity should be evaluated.

Myth: Period pain is always normal and should just be tolerated. Fact: Mild cramps are common, but severe pain that affects daily life may indicate a condition like endometriosis and should be evaluated by a healthcare provider.

When Irregular Periods Should Be Checked

See a healthcare provider if:

• Your periods have stopped for 3 or more months (and you are not pregnant or on hormonal contraception).
• Your cycle is consistently shorter than 21 days or longer than 35 days.
• Your periods have become much heavier or more painful than usual.
• You are bleeding between periods.
• You have reached age 16 and have not started menstruating.