Irregular Periods: Common Causes and When to Seek Help

22 Sep 2025

Most women experience changes in their menstrual cycle from time to time. Stress, travel, or even a new exercise routine can occasionally cause a late or early period. But if your cycles are frequently irregular, unusually heavy, or absent altogether, it may be a sign that something more is going on.

In this article, we’ll look at the common causes of irregular periods, when it’s considered normal, and when it may be worth seeing a doctor.

What Counts as an Irregular Period?

A typical menstrual cycle lasts between 21 and 35 days, with bleeding usually lasting 3–7 days. Your period is considered irregular if:

• The cycle length varies significantly month to month
• You often miss periods without being pregnant
• Periods are unusually heavy or light
• Bleeding occurs between periods
• Periods last longer than a week

One-off changes are usually nothing to worry about, but patterns of irregularity deserve more attention.

Common Causes of Irregular Periods

1. Stress and Lifestyle Changes

Stress affects hormone levels, which can disrupt the menstrual cycle. Significant weight loss, weight gain, or excessive exercise can also affect ovulation and cause irregularity.

2. Polycystic Ovary Syndrome (PCOS)

PCOS is a common condition that can cause irregular or absent periods, acne, excess hair growth, and difficulty with fertility. It occurs when hormone imbalances affect ovulation.

A PCOS Profile can help identify whether this condition is contributing to your symptoms.

3. Thyroid Disorders

Both overactive and underactive thyroid problems can disrupt menstrual cycles. Women may also experience weight changes, fatigue, or hair loss.

A Thyroid Function Test is often recommended when periods are irregular.

4. Perimenopause

In the years leading up to menopause, hormone fluctuations may cause cycles to become shorter, longer, or more unpredictable.

5. Medical Conditions

Other health issues, including diabetes, certain medications, or uterine conditions like fibroids, can also contribute to irregular cycles.

When to Seek Medical Advice

It’s sensible to see a doctor if you notice:

• Periods that stop for more than three months (without pregnancy)
• Very heavy or painful periods
• Bleeding between cycles
• Sudden changes in cycle length or pattern
• Irregular periods alongside other symptoms like fatigue, hair loss, or unexplained weight changes

You can arrange a Private GP Appointment or Gynaecology Consultation at South Kensington Medical & Dental for tailored advice.

Investigations and Tests

If your cycles are irregular, your doctor may suggest:

• Hormone tests – To check for PCOS, menopause, or other imbalances
• Thyroid function tests – To rule out thyroid-related causes
• Ultrasound scans – To look for fibroids, ovarian cysts, or uterine abnormalities
• General health blood tests – To identify underlying conditions like anaemia or diabetes

At South Kensington Medical & Dental, we provide fast access to Women’s Health Tests and ultrasound assessments with our experienced gynaecologists.

Looking After Your Cycle Health

While medical support is important, lifestyle adjustments can also support more regular cycles. Maintaining a balanced diet, managing stress, exercising moderately, and avoiding excessive dieting or over-exercising can all help.

If irregularity is linked to an underlying condition, treatment options may include hormone therapy, medication, or lifestyle changes tailored to your needs.

Final Thoughts

Irregular periods are common, but they shouldn’t always be ignored. While occasional cycle changes are usually harmless, ongoing irregularity can be a sign of hormonal imbalance or an underlying condition that needs attention.

If you’re concerned about your menstrual cycle, seeking medical advice can give you reassurance and the right care.