Hormones & HRT - Thyroid & fertility
Fertility hormones: FSH, LH, AMH and more
Last updated 30 September 2026. How we write this .
FSH, LH and AMH reveal different parts of reproductive function. Their meaning depends on timing and context, and no hormone panel can predict fertility on its own.
Start here FSH, LH and AMH reveal different parts of reproductive function. Their meaning depends on timing and context, and no hormone panel can predict fertility on its own.
By the end, you will understand The signalling system behind reproduction FSH and LH: signals whose meaning changes AMH: ovarian reserve is not egg quality Where this information comes from Claim-cited evidence. Central research claims on this lesson are linked to specific studies or official guidance.
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FSH and LH help control egg development, ovulation and sperm production, while AMH provides information about the small growing follicles in the ovaries. These hormones answer different questions: none is a complete fertility score. Menstrual cycle timing, age, medicines and clinical history change how results should be understood, and AMH alone cannot predict natural conception or egg quality.
The signalling system behind reproduction
Reproductive hormones work through a feedback system linking the brain and reproductive organs. The hypothalamus releases pulses of gonadotrophin-releasing hormone, or GnRH. These pulses prompt the pituitary gland to release follicle-stimulating hormone, FSH, and luteinising hormone, LH. The ovaries or testes respond, then send hormonal signals back to regulate further release.
In the ovaries, FSH supports follicles, the small structures containing immature eggs. Developing follicles produce oestradiol, a major form of oestrogen, and inhibin, which helps restrain FSH release. This feedback helps coordinate follicle development rather than allowing every follicle to progress together.
In the testes, LH stimulates testosterone production, while FSH supports the Sertoli cells that help developing sperm mature. Testosterone and inhibin provide feedback to the brain and pituitary. These mechanisms are well established through human physiology and clinical research, but understanding the signalling system does not make a single blood result a reliable prediction of conception.
FSH and LH: signals whose meaning changes
During the early part of a menstrual cycle, FSH supports a group of growing follicles. Usually, one becomes dominant. As it develops, its rising oestradiol output initially restrains FSH. Sustained high oestradiol then changes the feedback response, helping trigger an LH surge that precedes ovulation.
An LH rise can therefore be normal near ovulation but mean something different at another point in the cycle. FSH also changes across the cycle and between cycles. A laboratory reference range is only useful when it matches the physiological situation being assessed.
Higher FSH can reflect reduced feedback from the ovaries. Low or apparently normal FSH and LH can accompany reduced signalling from the hypothalamus or pituitary, including in some people experiencing low energy availability. These are patterns requiring context, not diagnoses that can be read directly from a number.
FSH has historically been marketed as an ovarian reserve test. Current NICE fertility guidance advises against using it to predict ovarian response or the outcome of assisted conception. That does not make FSH irrelevant: alongside other findings, it can help clinicians investigate absent periods or disrupted reproductive signalling.
AMH: ovarian reserve is not egg quality
Anti-Mullerian hormone, or AMH, is produced by cells surrounding eggs in small growing ovarian follicles. Its concentration provides an indirect marker of the follicle population, which relates to ovarian reserve. It is not a direct count of every egg remaining in the ovaries.
AMH varies less across the menstrual cycle than FSH or oestradiol, but it is not perfectly fixed. Laboratory methods, biological variation and hormonal contraception can affect results. Comparisons between reports also require attention to units: different-looking numbers may represent the same concentration.
Its clearest clinical value is helping anticipate ovarian response during assisted conception. Clinical studies support an association between AMH and the number of eggs likely to be collected. Predicting that response is different from predicting whether an embryo will develop successfully or a baby will be born.
Egg quality describes developmental potential, including the likelihood of chromosomal abnormalities. AMH does not measure that directly. Age remains important even when AMH appears reassuring. A low AMH result does not establish that natural conception is impossible, and a high result does not guarantee it.
Ovarian reserve, ovulation, egg quality and the chance of a live birth are different outcomes. A test can provide useful information about one while saying little about the others.
Oestradiol, progesterone and other relevant hormones
Oestradiol helps build the uterine lining and participates in the feedback controlling ovulation. Because it changes through the cycle, it can help explain an FSH result. For example, stronger oestradiol feedback can suppress FSH, so an apparently unremarkable FSH value may not tell the whole story.
After ovulation, the emptied follicle becomes the corpus luteum and produces progesterone. A progesterone measurement at an appropriate point in the cycle can support evidence that ovulation occurred. The relevant timing depends on the person's cycle, rather than one calendar day that suits everyone.
Progesterone is released in pulses, so its concentration can change substantially over a short period. One measurement cannot reliably grade the entire phase after ovulation or establish the quality of an egg. Evidence of ovulation also does not establish that the fallopian tubes are open or sperm function is adequate.
Prolactin can suppress reproductive signalling when persistently elevated, but stress, pregnancy and medicines can also influence it. It is not automatically a useful addition to every fertility panel. Thyroid function can affect menstrual patterns too; the separate lesson Understanding TSH and thyroid blood tests explains that system.
Human chorionic gonadotrophin, or hCG, is the hormone detected by pregnancy tests. It supports the corpus luteum early in pregnancy. A positive result indicates detectable hCG, but cannot by itself establish where a pregnancy is located or whether it is developing normally.
What the evidence can actually establish
The evidence for these hormones' biological roles is strong. Evidence for using them to predict an individual's reproductive future is more limited. Much test research comes from observational cohorts, including fertility clinic populations whose circumstances differ from those of people who have never tried to conceive.
An association across a study population does not automatically produce an accurate forecast for one person. A useful prediction must work in the population being assessed and add information beyond factors such as age and history. NICE specifically advises against using AMH to predict clinical pregnancy through spontaneous conception.
Test studies also need to distinguish outcomes. Predicting egg collection, detecting ovulation and predicting live birth require different evidence. Randomised trials can examine whether a testing strategy improves decisions or outcomes; simply showing that a marker correlates with something does not establish that widespread screening helps.
Who these tests apply to
Hormone testing can contribute to investigating irregular or absent periods, suspected disruption of ovarian or testicular function, or difficulties conceiving. The appropriate questions differ for someone with predictable cycles, someone without periods and someone undergoing assisted conception. Broad panels can generate incidental results without resolving the original concern.
Polycystic ovary syndrome can involve higher AMH because there may be more small follicles. That does not mean higher fertility. An LH-to-FSH ratio is not a standalone diagnostic test, and AMH cannot be interpreted as a diagnosis without the wider assessment.
Hormonal contraception, pregnancy, breastfeeding, perimenopause and prescribed hormones alter the context. Results from these situations cannot simply be compared with those from an untreated menstrual cycle. People taking hormones or other medicines should discuss interpretation with their care team and should not change medicines based on a consumer device.
Where conception involves partners, assessment considers both partners and their clinical histories. Semen analysis provides information that hormone testing cannot replace. Equally, ovarian hormone results cannot rule out problems involving the uterus or fallopian tubes. The assessment should reflect the people and reproductive route involved.
Judging claims and recognising limits
A claim that a panel reveals your 'fertility age' compresses several separate biological questions into one appealing label. Before accepting it, examine what was actually measured and what outcome the supporting research assessed.
Does the claim concern ovulation, ovarian response, natural conception or live birth? Were participants similar in age and circumstances to the people being offered the test? Were cycle timing, medicines, laboratory methods and units considered? Was the prediction checked in an independent population? Does the result improve a meaningful decision, or mainly create reassurance or alarm? The NHS advises seeing a GP if you have not conceived after a year of trying. Women aged 36 and over, and anyone who already knows they may have fertility problems, should see a GP sooner. A GP can start investigations and refer to NHS fertility services, and what is available depends on your local integrated care board.
Some symptoms mean home testing or waiting for another result is the wrong route. NHS advice is to contact a GP or NHS 111 if pregnancy is possible and symptoms such as one-sided lower abdominal pain or unusual bleeding occur, even without a positive test. Sudden severe abdominal pain with dizziness, fainting or collapse warrants calling 999.
This lesson is general education, not medical advice, and is not a recommendation to start, stop or change any hormone treatment. Your GP, practice nurse or a specialist can discuss what fits your history.
Related in this classroom The studies behind this page Investigation of fertility problems and management strategies - NICE guideline NG257, 2026Sources for this classroom
Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.