Most women will experience some variation in their menstrual cycle during their lifetime. Occasional irregularity is usually harmless, but persistent changes in the pattern, frequency, duration, or heaviness of periods can signal an underlying condition that benefits from investigation. This article explains what counts as an irregular period, the common causes, and when to seek specialist advice.
What Counts as an Irregular Period?
A normal menstrual cycle typically ranges from 21 to 35 days, with periods lasting up to 7 days. Irregularity covers a range of patterns that fall outside what is typical for a given woman, including:
- A cycle consistently shorter than 21 days or longer than 35 days
- Significant variation from month to month — for example, a difference of more than 7 to 8 days between one cycle and the next
- Periods lasting longer than 7 days
- Very heavy bleeding (such as soaking through a pad or tampon within an hour)
- Bleeding between periods
- Bleeding after sex
For many women, what appears irregular is simply their normal baseline. However, a change from your usual pattern — particularly if it is persistent — is worth discussing with a specialist.
Common Causes of Irregular Periods
There are many potential reasons why periods become irregular. Some are related to hormonal conditions, others to structural changes, lifestyle factors, or normal physiological transitions.
- Polycystic ovary syndrome (PCOS) — one of the most common hormonal conditions in women of reproductive age, PCOS affects ovulation and frequently causes irregular or infrequent periods. Read more on our PCOS specialist page.
- Thyroid disorders — both an underactive and overactive thyroid can affect the menstrual cycle. A simple blood test can check thyroid function.
- Perimenopause — the hormonal transition before menopause commonly causes changes in cycle length and flow. If you are in your 40s and noticing changes, see our perimenopause article for more information.
- Stress and lifestyle factors — significant psychological or physical stress can disrupt the hormonal signals that regulate the menstrual cycle, leading to delayed or absent periods.
- Significant weight changes — both substantial weight gain and weight loss can affect hormone levels and disrupt ovulation.
- Excessive exercise — very high levels of physical activity, particularly in combination with low body weight or restricted nutrition, can suppress the menstrual cycle.
- Fibroids — non-cancerous growths in the uterus that can cause heavy, prolonged, or irregular periods. Read more on our fibroids page.
- Endometriosis — tissue similar to the uterine lining grows outside the uterus, which can cause irregular and painful periods. Read more on our endometriosis page.
- Hormonal contraception changes — starting, stopping, or changing contraception (including the pill, implant, or intrauterine system) can alter the menstrual pattern, sometimes for several months.
- Pregnancy — including early pregnancy, which may not yet be apparent. A missed period is one of the first signs of pregnancy.
- Cervical or uterine conditions — conditions such as polyps, certain infections, or, less commonly, cervical or uterine abnormalities can cause irregular or intermenstrual bleeding. These are uncommon but important to rule out.
When to See a Specialist
Many cases of irregular periods can be investigated and managed effectively with a thorough assessment. It is worth booking a consultation if:
- Your periods have suddenly become irregular after previously being regular
- Your cycle is consistently shorter than 21 days or longer than 35 days
- Periods are lasting longer than 7 days
- You are experiencing very heavy bleeding — for example, soaking a pad or tampon every hour for two or more hours
- You are bleeding between periods
- You are bleeding after sex
- You are bleeding after menopause
- You are having irregular periods and are finding it difficult to get pregnant
- You have pelvic pain alongside irregular periods
These symptoms do not necessarily indicate a serious condition, but they do warrant investigation to identify the cause and put appropriate management in place.
How We Investigate Irregular Periods
At AristoGp, Dr Anastasia Mermigka — Consultant Gynaecologist (GMC 7640566) — provides a thorough and structured approach to investigating irregular periods. Your appointment will typically include:
- Full clinical history — a detailed discussion of your menstrual pattern, symptoms, medical background, and any relevant lifestyle or reproductive history
- Clinical assessment — a focused gynaecological assessment as appropriate
- Pelvic ultrasound — available on the same day as your consultation, a pelvic ultrasound can assess the uterus and ovaries in detail. The Consultation + Pelvic Ultrasound package is available from £270
- Blood tests — where indicated, these may include hormonal profile, thyroid function, and iron studies
- A clear management plan — explaining findings and outlining next steps, whether that is further investigation, treatment, or reassurance
Consultation Fees
- Face-to-Face Gynaecology Consultation (45 min) — £180
- Consultation + Pelvic Ultrasound — £270
- Follow-up Appointment — £100
The clinic is located at 1–5 Portpool Lane, London EC1N 7UU, approximately 3 minutes from Chancery Lane Underground station.
Book Your Appointment
To arrange an assessment for irregular periods with Dr Mermigka, use the booking button below or message the clinic via WhatsApp.
Book a Gynaecology Consultation
You may also find the following pages helpful:
Private Gynaecologist London | Private Ultrasound Scan London | About Dr Anastasia Mermigka
