Irregular periods: causes and when to see a doctor

Irregular periods can follow changes in contraception, stress or substantial weight changes; pregnancy and conditions affecting hormones are other possible explanations. They are not usually a sign of a problem, but the NHS advises seeing a GP if they’re irregular or your usual pattern changes.

An early period, a long gap and spotting between periods describe different changes, with potentially different explanations. ACOG distinguishes changes in timing, bleeding between periods and unusually heavy flow. Dates alone cannot identify the cause, and you don’t need a likely explanation before booking an appointment.

If you’re mainly concerned about the gap between period starts, how long a normal menstrual cycle lasts compares the published ranges.

Changes to take to your GP

Arrange a GP appointment if:

• Your periods are irregular, or your usual pattern has changed.
• Bleeding lasts longer than 7 days, or is unusually heavy.
• You bleed between periods, after sex or after menopause.
• You have missed three periods in a row.
• A missed or irregular period comes with symptoms such as weight changes, tiredness or new facial hair growth.
• Irregular periods are making it harder to become pregnant, if that is something you want.

The NHS covers these reasons in its advice on irregular periods and missed periods, alongside ACOG’s bleeding guidance. Pain or bleeding that keeps you from ordinary activities also deserves help.

Bring the information you already have. Irregular cycles: what to log and when to ask can help you organise it, but collecting a complete diary isn’t a condition of booking care.

Pregnancy, breastfeeding and a missed period

A missed period can be an early sign of pregnancy. Breastfeeding can also delay periods returning after birth, as described in the NHS missed-periods guidance and the Office on Women’s Health’s cycle guide.

You may or may not ovulate while breastfeeding. If you want to avoid pregnancy, ask about suitable contraception: having no periods does not mean you can rely on being protected. Irregular cycles can involve less regular ovulation, but pregnancy is still possible.

If pregnancy could explain a missed period, use a test. Bleeding doesn’t rule it out: ectopic-pregnancy bleeding can be mistaken for a period. Bleeding with pain and possible pregnancy needs prompt advice.

When to test

If you don’t know when your period is due, test at least 21 days after the last unprotected sex. Repeat a negative result after a few days if you still think pregnancy is possible. Contact your GP after a second negative result if your period hasn’t arrived. Follow the NHS pregnancy-test guidance and the test instructions.

Contraception and medicines can change bleeding

Hormonal contraception can change bleeding, including bleeding outside the time you expected. Starting or stopping the contraceptive pill can affect menstruation. The NHS also lists the progestogen-only pill, injection and hormonal coil among possible causes of irregular periods.

Some changes affect flow more than timing. A copper intrauterine device (IUD) can make bleeding heavier, particularly during the first year of use. Blood-thinning medicines and aspirin can also cause heavier menstrual bleeding, as set out in ACOG’s guide to abnormal uterine bleeding.

Ask the professional who prescribes your medicine or contraception what bleeding changes to expect with that particular treatment. Mention new or troublesome bleeding, even if you think it may be a side effect, so they can check it. Do not stop a prescribed medicine or change your contraceptive schedule without advice.

Periods at puberty and approaching menopause

Periods are more likely to be unpredictable when they first begin and during perimenopause, the transition towards menopause. Ovulation may not happen regularly at these stages, and cycles without ovulation can involve irregular or heavy bleeding.

During the transition to menopause, you may miss periods and then bleed again. The bleeding’s length or heaviness may also change. The Office on Women’s Health describes these changes across the reproductive years.

Discuss abnormal or troublesome bleeding even when changes are expected at your age. ACOG specifically recommends this at stages when irregularity is common. Bleeding after menopause needs checking too; treat it as a reason to seek care, not as another returning period.

Stress, weight and exercise

Substantial weight gain or loss, stress and excessive exercise are among the possible causes of irregular periods. Recognising a stressful stretch or a change in training gives you something to mention at the appointment. Another cause may still need checking.

These changes aren’t something to blame yourself for. Describe what has been happening and ask, “Could this change in routine be relevant?” You can discuss it without having to prove a connection or arrive with a self-prescribed diet or exercise programme.

For a closer look at the evidence for each, read stress, sleep, exercise and your cycle.

Conditions your GP may consider

Polycystic ovary syndrome (PCOS) can affect ovulation and lead to irregular periods. Current NHS guidance calls this condition polyendocrine metabolic ovarian syndrome (PMOS); some other guidance still uses PCOS. Thyroid problems can also affect menstrual timing.

Both an underactive and an overactive thyroid are possible causes. Other conditions affect bleeding differently: ACOG describes fibroids and polyps, which are non-cancerous growths, as causes of irregular or heavy bleeding.

An assessment can consider more than one explanation. Tell your GP about other symptoms alongside the period change, particularly tiredness, facial hair growth, weight gain and changes in skin. You don’t need to match a whole symptom list to ask for help.

Get urgent advice for these symptoms

Possible pregnancy with unusual bleeding or lower abdominal pain, particularly on one side, needs prompt medical advice even without a positive test. Contact a GP urgently or NHS 111 in the UK, or your local urgent medical service elsewhere.

Sudden intense abdominal pain with severe dizziness or fainting can be an emergency. Call 999 in the UK, or your local emergency number, or go to an emergency department (A&E in the UK).

ACOG also advises emergency care if you are changing pads or tampons every hour for more than 2 hours in a row and also have chest pain, shortness of breath and light-headedness or dizziness. Seek help immediately.