Hormones in Female Reproduction: What Goes Wrong

In most cases it is not one hormone being low — it is that ovulation is not happening reliably, and several different upstream problems produce that same result. Four causes account for most of what is found: polycystic ovary syndrome, thyroid disease, a raised prolactin, and low hypothalamic drive from very low body weight, heavy training or illness.

They are separated by a short set of tests rather than by symptoms, because the symptoms overlap. What matters for you is that these four have different treatments, so the test result changes what happens next.

A missed or late period is also, commonly, an early pregnancy. That is ruled out first, before any of this.

Three levels, in order. The hypothalamus releases GnRH in pulses. Those pulses make the pituitary release FSH and LH. FSH recruits a cohort of ovarian follicles, which grow and make estradiol.

Estradiol initially feeds back negatively and damps FSH down, which is how one dominant follicle wins and the rest regress. Then, at a high enough level and for long enough, that feedback flips positive and triggers the LH surge. Ovulation follows the start of the surge by roughly a day and a half. The emptied follicle becomes the corpus luteum and makes progesterone, which holds the lining steady; if there is no pregnancy it fades, progesterone falls, and the lining sheds.

Two practical consequences fall out of that. First, the pulses matter as much as the amounts: continuous rather than pulsatile GnRH suppresses FSH and LH instead of driving them, which is exactly how GnRH agonist drugs shut the axis down in IVF. Second, progesterone only appears after ovulation, which is why a mid-luteal progesterone is used to confirm ovulation happened at all.

If you want this one level deeper on the estrogen side, that is covered separately in what estrogen does across one cycle.

A typical first round is short. What each is for:

• TSH and free T4 — thyroid disease disturbs cycles in both directions and is cheap to exclude.
• Prolactin — a raised prolactin suppresses GnRH, which lowers FSH and LH and stops ovulation. It has its own treatment, so finding it changes the plan.
• Total testosterone, sometimes with SHBG — for the hyperandrogenism limb of the PCOS criteria.
• FSH, LH and estradiol on day 2 or 3 — mainly to tell an ovarian problem (FSH high) from a pituitary or hypothalamic one (FSH and LH both low).
• Pelvic ultrasound — antral follicle count and ovarian morphology. In 2023 AMH became an accepted alternative to ultrasound in adults for defining polycystic ovarian morphology.
• Mid-luteal progesterone — confirms that ovulation occurred in that cycle.

The 2023 PCOS guideline is worth knowing on one point here: where irregular cycles and hyperandrogenism are both present, diagnosis is simplified and neither ultrasound nor AMH is required. It also recommends not doing both AMH and ultrasound, specifically to limit overdiagnosis. If you are being sent for both, that is a fair question to ask.

It depends on the cause, and that is the argument for testing before treating.

1. PCOS with anovulation and no other infertility factor: the 2023 guideline recommends letrozole as the first-line drug, and recommends it ahead of clomiphene citrate. Note the guideline's own caveat at 5.3.2 — letrozole is still off-label for this indication in many countries, and where it is not permitted other ovulation induction agents are used.
2. Thyroid disease: the thyroid is treated, and cycles commonly settle without any fertility drug.
3. Raised prolactin: the cause of the raised prolactin is addressed. Ovulation induction is not the starting point.
4. Low hypothalamic drive: restoring energy availability and weight is the treatment. Drugs that push the pituitary do not fix an axis that has been switched off deliberately.

None of the above is IVF, and for anovulation alone it usually should not be. Ovulation induction with timed intercourse is the cheaper and simpler route, and the guideline treats IVF as a later step rather than a first one.

Where the honest answer is that the evidence is thinner than the marketing:

• It does not establish that a single hormone is 'imbalanced' and needs correcting. There is no test that reports an imbalance; there are tests that identify specific named conditions.
• It does not establish luteal phase deficiency as a cause of infertility. ASRM's 2021 committee opinion states that it has not been proven to be an independent entity causing infertility or recurrent pregnancy loss.
• It does not establish that ovarian reserve tests predict whether you will conceive. ASRM's 2020 committee opinion states these markers are poor predictors of reproductive potential independently from age, and Steiner's cohort of 750 women aged 30-44 found a raised FSH was not associated with reduced fertility.
• It does not establish that a supplement, detox or diet protocol restores ovulation. Where energy availability or weight is the cause, changing that is treatment; a branded product is not the same claim.
• It does not establish that a normal set of hormones means nothing is wrong. Tubes, the uterus and semen quality are not measured by any of these tests.

Being handed a list of hormone names with no sense of which one matters is genuinely disorienting, and that is a problem with how results are reported rather than a sign that your case is complicated.

No. Nothing here is a reason to stop something a doctor has prescribed, and stopping an ovulation induction drug or a thyroid medicine part-way through is its own risk. Your doctor has your history, your ultrasound and your examination, none of which an article has.

What this page is useful for is asking better questions at the next appointment: which cause was found, which test showed it, what this drug is meant to change, how long before we know whether it worked, and what happens if it does not.

• Understanding anovulation
• Reading a day-3 FSH, LH and estradiol panel
• What estrogen does across one menstrual cycle
• PCOS and its effect on fertility
• Thyroid and fertility: the connection
• Ovulation induction: process and success rates