Irregular Periods

A "normal" cycle is anywhere from 21 to 35 days, and perfectly regular cycles are less universal than people assume. What matters is a change from your own pattern that persists.

Irregularity in the first couple of years after periods start, and again in the years approaching menopause, is expected. In between, a persistent change usually has an identifiable cause.

Pregnancy. Always the first thing to exclude, including where you believe it impossible.

Hormonal

• PCOS — the commonest cause of irregular or absent periods in women of reproductive age. Often with acne, excess hair growth or difficulty losing weight
• Perimenopause — cycles becoming shorter, longer, heavier or lighter, typically from the mid-forties but sometimes earlier
• Thyroid disease — both under- and overactive disrupt cycles, and both are easily tested
• Raised prolactin — can stop periods entirely and occasionally indicates a pituitary problem needing imaging

Lifestyle and body — significant weight loss or gain, intensive exercise, severe stress, and eating disorders, which commonly stop periods and are not confined to any body size.

Structural — fibroids and polyps, more often causing heavy or intermenstrual bleeding than irregularity.

Contraception — the coil, implant, injection and progestogen-only pill all change bleeding patterns, usually harmlessly.

The consultation covers your actual cycle history — tracking app data is genuinely useful here — alongside weight change, exercise, stress, contraception and any acne or hair changes.

Testing depends on the picture: a hormone panel covering LH, FSH, testosterone, SHBG and prolactin where PCOS or perimenopause is likely, thyroid function as a matter of course, and HbA1c and insulin where PCOS is suspected — because the metabolic side is frequently not measured and matters as much as the sex hormones.

Where the picture suggests fibroids, polyps or a structural cause, we arrange pelvic ultrasound and gynaecology referral.

What actually counts as irregular?

A normal cycle runs 21 to 35 days from the first day of one period to the first day of the next, with individual cycles varying by no more than about seven to nine days. Periods themselves last two to seven days.

Irregular means: consistently shorter than 21 or longer than 35 days, wide variation month to month, three or more months without a period, or a clear change from what has been normal for you. Cycles are often naturally irregular in the first couple of years after periods start and in the years approaching the menopause.

Could it be PCOS?

It is the commonest hormonal cause of irregular periods. Diagnosis requires two of these three: irregular or absent ovulation; signs of raised male-type hormones — either on a blood test, or clinically as acne or excess hair growth; and polycystic-appearing ovaries on ultrasound.

Two points that are often got wrong: you do not need an ultrasound if you already meet the other two criteria, and the scan is unreliable within a few years of periods starting, because many young women's ovaries look that way normally. Note also that PCOS is not a matter of having cysts — the follicles seen are not cysts, despite the name.

What tests do I need, and when in my cycle?

Timing matters for some of them:

• FSH, LH, oestradiol — days 2 to 5 of the cycle, if you are having periods
• Progesterone to confirm ovulation — seven days before the expected period, which is day 21 only in a 28-day cycle
• Testosterone and related hormones — any time, for PCOS
• Thyroid function and prolactin — any time. Both are common, easily treated causes of irregular or absent periods and should always be checked
• Ferritin if bleeding is heavy

Is AMH a test for PCOS or fertility?

AMH is not a diagnostic test for PCOS, though it is often sold as one. It gives an estimate of ovarian reserve — roughly how many eggs remain — which is useful in fertility planning and before IVF.

What it does not do is predict whether you can conceive naturally. A low result in a woman with regular cycles is not a verdict on her fertility, and it causes a great deal of unnecessary distress when sold as a standalone check.

How do I know if it's perimenopause rather than PCOS?

Chiefly by age and direction of travel. Perimenopause typically begins in the forties, with cycles first becoming shorter and then increasingly erratic, accompanied by hot flushes, night sweats, sleep disruption, mood change and brain fog. PCOS usually begins soon after periods start, with long cycles from the outset plus acne or excess hair.

Over 45, perimenopause is diagnosed on symptoms — blood tests are unhelpful, because hormone levels swing wildly from week to week. Under 45, testing is worthwhile.

My contraception has made my bleeding unpredictable. Is that a problem?

It is expected, not a malfunction. The implant, injection, progesterone-only pill and hormonal coil all commonly cause irregular bleeding, particularly in the first three to six months, after which many people settle into light bleeding or none at all.

It does not mean the contraception has failed. If it persists and bothers you, there are effective ways to manage it — worth asking about before abandoning a method that is otherwise working well.

My periods stopped when I started training seriously. Is that fine?

No — it is a signal worth taking seriously, even though it is often welcomed. Periods stopping in the context of hard training, restricted eating, or weight loss usually means the body is not getting enough energy for what it is being asked to do.

The consequence that matters is bone density, which falls with prolonged low oestrogen and does not fully recover later. It is common in endurance athletes and dancers and consistently under-recognised. It is treatable, and the treatment is usually more food rather than more medicine.

How heavy is too heavy?

If your period dictates what you can do, it is too heavy — that is the practical definition, and it is more useful than any measurement. Concrete markers: soaking through a pad or tampon in under two hours, needing double protection, passing clots larger than a 10p piece, flooding onto clothes or bedding, or planning around it.

Heavy periods are the leading cause of iron deficiency in women, and are frequently normalised for years. Effective treatments exist — tranexamic acid, hormonal options, a coil — and none of them requires putting up with it.