Irregular Periods: Common Causes and When You Should See a Gynaecologist

Introduction

Almost every woman experiences an irregular period at some point — but when irregularity becomes a pattern, it's worth understanding why. Menstrual cycles are sensitive to a wide range of influences, from hormones to stress to underlying medical conditions. This guide walks through the common causes and helps you know when it's time for a proper evaluation rather than waiting things out.

Key Takeaways

• A "normal" cycle can range from about 21 to 35 days — irregularity means a pattern that consistently falls outside this, or unpredictable timing.
• Common causes include PMOS/PCOS, thyroid disorders, pregnancy, stress, significant weight changes, and perimenopause.
• Some medications and other gynaecological conditions can also affect cycle regularity.
• Self-medicating to induce periods isn't appropriate without first understanding the underlying cause.
• Persistent irregularity, especially with other symptoms, warrants a gynaecological evaluation.

What Counts as Menstrual Irregularity?

Cycles vary from person to person, but general patterns that suggest irregularity include:

• Cycles consistently shorter than 21 days or longer than 35 days
• Unpredictable timing that varies significantly month to month
• Periods that are unusually heavy, prolonged, or associated with large clots
• Absence of periods for three months or more (when not pregnant)
• Bleeding between periods

A single irregular cycle is common and often not significant on its own — the pattern over time matters more than any one occurrence.

Common Causes

PMOS/PCOS

Polyendocrine Metabolic Ovarian Syndrome (PMOS) — the updated name for Polycystic Ovary Syndrome (PCOS) — is one of the most common causes of irregular ovulation and periods. We cover this in detail in our PMOS/PCOS guide.

Thyroid Disorders

Both an underactive and overactive thyroid can disrupt the hormonal balance that regulates menstruation, which is why thyroid function is often checked as part of an irregular-periods evaluation.

Pregnancy

A missed or unusually light period can be an early sign of pregnancy and is generally one of the first things ruled out during evaluation.

Stress

Significant physical or psychological stress can affect the hypothalamic signals that drive ovulation, sometimes delaying or skipping periods entirely.

Weight Changes

Both significant weight loss and weight gain, especially when rapid, can affect hormone levels enough to disrupt cycle regularity.

Perimenopause

As women approach menopause, hormonal shifts commonly cause cycles to become irregular before periods stop altogether. This is a normal transition, though it's still worth discussing with your gynaecologist to distinguish it from other causes.

Medication-Related Causes

Certain medications, including some hormonal contraceptives and other prescription drugs, can influence cycle patterns. If you've recently started or stopped a medication and noticed changes, mention this to your doctor.

Other Gynaecological Causes

Conditions such as fibroids or endometrial issues can also cause irregular or heavy bleeding, and are part of what a gynaecologist evaluates for.

Why Evaluation Matters

Because so many different things can cause irregular periods, treating the irregularity itself — for example, by trying to induce a period without medical guidance — can mask an underlying issue that actually needs attention. Proper evaluation helps identify the actual cause, which then guides the right approach.

What a Doctor May Ask, and Possible Tests

A typical evaluation includes:

• A detailed menstrual history — cycle length, flow, associated symptoms, and how long the irregularity has been happening
• General health history, including recent weight changes, stress, and medications
• A clinical examination
• Blood tests, often including thyroid function and other relevant hormone levels
• Pelvic ultrasound, when appropriate, to assess the uterus and ovaries

Not every test applies to every patient — your doctor will tailor the evaluation to your specific history and symptoms.

When to See a Gynaecologist

Book an evaluation if:

• Irregularity has persisted for several cycles
• You're experiencing very heavy bleeding, severe pain, or bleeding between periods
• Your periods have stopped for three months or more and you're not pregnant
• You're trying to conceive and cycle irregularity is a concern
• Irregular periods are accompanied by other symptoms like acne, hair growth changes, or unexplained weight changes

If you're also considering fertility, our fertility evaluation guide explains when that kind of assessment is typically recommended.