For a pregnancy to happen, an egg has to be released. Anovulation means that this is not happening — either at all, or not reliably. It is one of the most common reasons women have difficulty conceiving, and it is also one of the most treatable.

How the cycle normally works

Each month the brain releases hormones that tell the ovaries to prepare an egg. Follicle-stimulating hormone (FSH) grows the follicles that contain eggs; a surge of luteinising hormone (LH) then triggers one to release its egg. After release, the empty follicle produces progesterone, which prepares the womb lining. If no pregnancy occurs, progesterone falls and a period follows.

A typical cycle runs 21 to 35 days, with ovulation roughly two weeks before the next period is due.

Signs that ovulation may not be happening

  • Periods that are irregular, unpredictable, or very far apart
  • Periods that have stopped altogether
  • Very light or very heavy bleeding
  • No mid-cycle signs — no change in cervical mucus, no mid-cycle twinge

Regular, predictable periods usually mean you are ovulating. Irregular ones do not always mean you are not — but they are worth investigating.

What causes it

  • Polycystic ovary syndrome (PCOS) — by some distance the commonest cause. See our guide to PCOS.
  • Thyroid problems — both underactive and overactive
  • Raised prolactin, a hormone that can suppress ovulation
  • Being significantly over- or underweight
  • Excessive exercise or significant physical or emotional stress
  • Reduced ovarian reserve, or approaching menopause

How it is confirmed

Two tests are commonly used, and the timing of both depends on your cycle length.

Progesterone blood test

Progesterone rises only after an egg has been released, so a raised level confirms ovulation happened. The test is taken in the mid-luteal phase — about 7 days before your next period is due.

You will often hear this called the “day 21 test”. That is correct only if your cycle is a regular 28 days. If your cycle is 35 days, the right day is around day 28; if it is 24 days, around day 17. Getting this wrong is a common reason for a falsely reassuring or falsely alarming result — so tell whoever arranges the test how long your cycle actually is.

Ultrasound tracking

A transvaginal scan can watch a follicle grow and then confirm it has released. In a regular 28-day cycle, scanning often begins around day 11; again, this shifts with cycle length. Sometimes a series of scans is used across one cycle.

Blood tests for thyroid function, prolactin and other hormones are usually done alongside these, to look for a treatable cause.

Treatment

Weight and lifestyle first

Where anovulation relates to weight — and particularly in PCOS — even a modest, sustained weight loss can restore ovulation on its own, without any medication. This is genuinely effective treatment, not a preliminary to the real thing, and it is worth taking seriously before moving to tablets.

Tablets to induce ovulation

  • Letrozole is used first-line.
  • Clomifene citrate is used in selected patients.

Both work by prompting the body to produce more of the hormones that drive ovulation. Cycles are usually monitored, particularly at first.

Injections

If tablets do not work, gonadotrophin injections (FSH, or human menopausal gonadotrophin) are the second-line option. These need careful monitoring, because they carry a higher risk of multiple pregnancy and of over-stimulating the ovaries.

Any underlying cause — thyroid disease, raised prolactin — is treated in its own right, and doing so often restores ovulation without fertility drugs at all.

For more detail see our guide to ovulation induction.

When to seek help

See a doctor if you have been trying for a year without success, or six months if you are over 35. Come sooner if your periods are irregular or absent — there is no value in waiting a year when the cycle itself is telling you something.

The bottom line

Anovulation is common, identifiable with simple tests, and treatable in most women — often with weight and lifestyle change alone, and otherwise with tablets that work well. The key practical point is that the tests must be timed to your cycle, not to a standard 28-day one.

References

  1. National Institute for Health and Care Excellence. Fertility problems: assessment and treatment. NG257. London: NICE; 2026. Available from: https://www.nice.org.uk/guidance/ng257
  2. National Health Service. Infertility [Internet]. NHS; [cited 2026 Jul 22]. Available from: https://www.nhs.uk/conditions/infertility/
  3. National Health Service. Fertility in the menstrual cycle [Internet]. NHS; [cited 2026 Jul 22]. Available from: https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/