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Hormones & cycles

Irregular periods

A symptom, never a diagnosis. The useful question is always: irregular because of what?

21–35days is a typical cycle

The gold band is roughly when ovulation happens.

01

What it actually is

A typical cycle runs somewhere between 21 and 35 days, and for most women the length is reasonably predictable from month to month. Cycles shorter than 21 days, longer than 35, varying by more than about a week each month, or disappearing for months at a time all count as irregular.

Irregular periods are not a diagnosis in themselves — they are the visible sign of something upstream. The whole job of the consultation is finding which cause applies to you, because the treatment for a thyroid problem looks nothing like the treatment for PCOS.

Occasional variation is normal, particularly in the first years after periods start and in the years approaching menopause. Persistent irregularity outside those windows is worth investigating.

28d28d28d28dA regular pattern24d47d25d62dWorth investigating21–35 days, predictablegaps that swing, or over 35 days
Three tracked months tell a doctor more than any single blood test. Note the first day of every period and bring the list.

For general understanding only. These are drawings, including the ultrasound view — they are built from typical measurements to explain the idea, and are not real scan images or a picture of your own baby.

02

What you might notice

  • Cycles consistently shorter than 21 days or longer than 35
  • Cycle length that swings by more than a week from month to month
  • Periods that stop for three months or more without pregnancy
  • Bleeding or spotting between periods
  • Bleeding after sex
  • Periods that suddenly become much heavier or much lighter than your normal

Don't wait for an appointment if…

  • Bleeding between periods or after sex
  • Any bleeding after menopause
  • Periods stopping for three months or more when you are not pregnant
  • Irregular cycles with milky nipple discharge, or with severe headaches or vision changes
03

The tests that are actually useful

Not everyone needs every test. This is what each one is for, so you know why it was ordered — or why it wasn't.

A blood testHormones, thyroid and iron — the numbers no scan can show.
An ultrasoundThe shape of the uterus, the thickness of the lining, and the follicles on each ovary.
A camera, sometimesA keyhole look inside, offered only when it would change the plan.

Not everyone needs all three. Each answers a different question — which is why a test you were not offered is often the right call.

A pregnancy testAlways first. It is the most common single explanation for a missed period and everything else follows from ruling it out.
Thyroid functionBoth an underactive and an overactive thyroid disturb the cycle, and both are straightforward to correct.
ProlactinRaised prolactin is an important and treatable cause of absent or irregular periods.
FSH, LH and oestradiolAssesses how the ovaries and the signals driving them are working, and helps identify the perimenopause.
AndrogensLooks for the hormonal picture of PCOS.
Pelvic ultrasoundIdentifies structural causes — polyps, fibroids in the cavity, or the follicle pattern of PCOS.
04

Treatment, in the order it's usually tried

  1. Start simpleLifestyle, pain relief, or a tablet — whatever is least disruptive to your life.
  2. Add if neededA hormonal option or a longer course, if the first step has not settled things.
  3. A procedureDay-case surgery when medicine cannot fix the structure causing the problem.
  4. Specialist routeFertility treatment or a referral, planned with you rather than sprung on you.

You move up a rung only if the one below it has not done the job — and you can stop at any step you are happy with.

Treat the cause, not the symptom

Correct the thyroid, address raised prolactin, manage PCOS, remove a polyp.

In most cases the cycle settles once the underlying reason is dealt with. Regulating the bleed while ignoring the cause is rarely the right first move.

Where lifestyle is driving it

Addressing significant weight change, very high training loads, disordered eating or sustained stress.

The body switches ovulation off when it reads the environment as unsafe. This is handled without judgement, and often with input from a dietitian.

Cycle regulation

Cyclical progesterone or combined hormonal contraception.

Used to give predictable bleeding and to protect the lining of the uterus where periods are very infrequent.

If you are trying to conceive

Ovulation tracking, and ovulation induction if you are not ovulating.

Irregular cycles make timing hard. Confirming whether you are ovulating at all changes the plan completely.

05

What you were probably told that isn't true

Going on the pill fixes irregular periods.
The pill creates a predictable withdrawal bleed. It manages the symptom, which is sometimes exactly right — but it does not treat what is causing it.
Irregular periods always mean PCOS.
PCOS is one common cause among several. Thyroid disease, prolactin, weight change and perimenopause all produce the same picture.
If your period is irregular you cannot get pregnant.
Irregular ovulation is unpredictable, not absent. Contraception is still needed if you do not want to conceive.
Next step

Bring this to someone who has time.

A 25–40 minute consultation, on video, with a doctor who will explain what applies to you specifically — and what doesn't.

This page is general information, not medical advice. Nothing here can diagnose you or replace an assessment of your own history, examination and results. If something here matches what you are experiencing, the next step is a consultation — not a conclusion. If you are in severe pain, bleeding heavily, or feel unwell, seek urgent care rather than waiting for an appointment. Awaiting final clinical review before publication.