Should I worry if my periods are irregular?

An occasional late or unusual period can happen to almost anyone.

Stress, illness, travel, changes in weight, medication, contraception and big life changes can all affect your cycle from time to time. But if your periods are often unpredictable, very far apart, unusually heavy, or missing for several months, it is worth paying attention.

Many people wait a long time before asking about irregular periods. They may assume it is stress, something that will settle on its own, or simply how their body works. Sometimes that is true. But when cycle changes keep happening, they can be a sign that ovulation is not happening regularly, or that something hormonal or gynaecological needs checking.

What counts as an irregular menstrual cycle?

A menstrual cycle is counted from the first day of one period to the first day of the next.

For many women, cycles are somewhere between 21 and 35 days. Some variation is normal, and your cycle does not need to be exactly the same length every month.

A cycle may be considered irregular if your periods are often shorter than 21 days, longer than 35 days, missing for several months, or difficult to predict from one cycle to the next.

Irregular cycles can also include bleeding patterns that feel unusual for you, such as spotting between periods, very heavy bleeding, or bleeding that lasts much longer than expected.

When can cycle changes be normal?

Not every change in your period means something is wrong.

It is common for cycles to be irregular during adolescence, especially in the first few years after periods begin. The hormonal system is still maturing, so ovulation may not happen regularly at first.

Cycles can also become less predictable during perimenopause, when hormone levels begin to fluctuate before menopause.

Temporary changes can happen during periods of stress, poor sleep, travel, illness, intense exercise, under-eating or significant weight change. The body is sensitive to these pressures, and ovulation can be delayed or missed as a result.

A short-lived change that settles again may not need investigation. A change that keeps happening, or becomes your new normal, is different.

How are irregular cycles linked to ovulation?

Ovulation is the release of an egg from the ovary. If ovulation is delayed, your period may arrive later than expected. If ovulation does not happen, your period may be missed altogether or bleeding may become unpredictable.

This is why irregular cycles can matter, especially if you are trying to conceive or want to understand your hormonal health.

Long gaps between periods can also mean the womb lining has more time to build up before it sheds. For some women, this can lead to heavier bleeding when a period does arrive. This is one reason some delayed periods can be heavier when they arrive.

Regular periods often suggest that ovulation is happening regularly, although this is not always guaranteed. If your cycle is often unpredictable, your doctor may want to understand whether ovulation is happening consistently and whether anything is disrupting it.

What can cause irregular periods?

There are many possible reasons for irregular cycles.

Some are temporary, such as stress, illness, travel, changes in routine or weight change. Others may need assessment and treatment.

Common causes include pregnancy, breastfeeding, contraception, PCOS, thyroid problems, high prolactin, perimenopause, significant weight loss, over-exercising, fibroids, polyps or other gynaecological conditions.

PCOS is one of the most common causes of irregular periods. It can affect ovulation and may also cause acne, increased facial or body hair, hair thinning, weight changes or difficulty getting pregnant.

Thyroid problems can also affect the menstrual cycle because thyroid hormones influence metabolism and reproductive hormone signalling.

This is why it is useful to look beyond the dates of your periods alone. Symptoms such as acne, hair growth, weight change, pelvic pain, heavy bleeding or bleeding between periods can help point towards the most likely cause.

What symptoms suggest irregular periods should be checked?

You do not need to wait until symptoms are severe before asking for advice.

It is worth speaking to a GP or gynaecologist if you notice:

• Periods that are regularly more than 35 days apart
• Periods that often come less than 21 days apart
• Fewer than 8 periods a year
• Periods that stop for 3 months or more
• Very heavy or prolonged bleeding
• Bleeding between periods or after sex
• Severe pelvic pain or worsening period pain
• Irregular periods with acne, excess facial or body hair, or hair thinning
• Unexplained weight changes
• Difficulty getting pregnant
• Symptoms that feel unusual for you or are affecting your quality of life

If pregnancy is possible and your period is late or missing, take a pregnancy test.

You should seek prompt medical advice if bleeding is very heavy, you feel faint or very weak, you have severe pelvic pain, or you may be pregnant and have pain or bleeding.

How are irregular cycles assessed?

A GP or gynaecologist will usually start by asking about your cycle.

They may ask when your periods started changing, how often you bleed, how heavy the bleeding is, whether you have pain, and whether you have symptoms such as acne, hair growth, hair thinning, weight changes, discharge or fertility concerns.

It can help to bring a cycle record if you have one. Even a few months of dates, bleeding patterns and symptoms can make the appointment more useful.

Depending on your symptoms, your doctor may suggest a pregnancy test, blood tests to check hormone levels, thyroid function, prolactin, iron levels or other markers. An ultrasound scan may be recommended if there is concern about PCOS, fibroids, polyps or another pelvic cause.

Not everyone needs every test. The assessment should be guided by your symptoms, age, medical history and what is most likely in your situation.

Irregular periods are worth checking when they stop feeling normal for you

One unusual period is often not a reason to worry.

But if your cycle has become persistently irregular, your periods have stopped, or your bleeding pattern has changed in a way that does not feel normal for you, it is worth getting checked.

Irregular periods can sometimes be a sign that ovulation, hormones or another part of your reproductive health needs attention. Getting advice early can help identify the cause, guide treatment if needed, and give you a clearer understanding of what is happening in your body.

About the author

Dr Nikki Ramskill is a General Practitioner specialising in women’s health, based in Milton Keynes and the founder of The Female Health Doctor Clinic. She supports women with PCOS, subfertility, premature ovarian insufficiency, menopause, period problems (including heavy periods), contraception, and hormone replacement therapy (HRT). She has over a decade of clinical experience providing personalised, comprehensive care for women across all life stages.