Fertility Labs Explained — What Actually Matters

Fertility labs look like alphabet soup until someone walks you through them. This is the clinician's tour.

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AMH — Anti-Müllerian Hormone

What it tells you: egg supply (quantity).

• Higher → more eggs remaining.
• Lower → fewer eggs remaining.
• Important: this does not measure egg quality. A low AMH at 32 is different from a low AMH at 42.

Can be drawn any day of the cycle. Useful for counseling and for predicting response to ovarian stimulation if IVF is on the table.

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FSH — Follicle-Stimulating Hormone

What it tells you: how hard your brain is having to push to recruit a follicle.

• Higher FSH → your body is working harder → typically lower ovarian reserve.
• Measured on cycle day 3 for accuracy, ideally alongside estradiol.

If estradiol is already elevated on day 3, it can artificially suppress FSH and mask a problem. Always interpret them together.

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LH — Luteinizing Hormone

What it tells you: ovulation signaling.

• The mid-cycle LH surge triggers ovulation.
• Chronically high LH relative to FSH (LH:FSH ratio > 2) is suggestive of PCOS.

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Estradiol (E2)

What it tells you: estrogen production from developing follicles.

• Day 3 estradiol contextualizes FSH.
• Mid-cycle estradiol rises before ovulation.
• Elevated early-cycle estradiol can be an early diminished-reserve signal.

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Progesterone

What it tells you: did you actually ovulate?

• Drawn ~7 days after suspected ovulation (often cycle day 21 in a 28-day cycle — adjust for your cycle length).
• A value above ~3 ng/mL confirms ovulation occurred; above ~10 ng/mL suggests a robust luteal phase.

This is the single most useful "did anything actually happen this cycle" marker.

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TSH (and free T4)

What it tells you: thyroid function.

Even mild hypothyroidism disrupts ovulation, implantation, and early pregnancy. For patients trying to conceive, I typically target TSH < 2.5 mIU/L rather than the standard < 4.5.

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A1c, fasting insulin, and metabolic markers

What they tell you: insulin resistance, often unrecognized.

Insulin resistance is one of the most common reversible drivers of subfertility — particularly in PCOS, but also in patients with no obvious PCOS features. Worth checking even when weight is normal.

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Prolactin

What it tells you: whether elevated prolactin is suppressing ovulation.

Common, easy to fix, often missed.

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Vitamin D and ferritin

Both quietly affect fertility and pregnancy outcomes. Both routinely run low. Both easy to correct.

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How I put it together

A single panel is a snapshot. The story usually shows up over 2–3 cycles of targeted testing — day 3 panel, mid-cycle, and luteal phase progesterone — combined with a thoughtful history.

What I'm trying to answer:

1. Are you ovulating?
2. If yes, is the luteal phase adequate?
3. What's the ovarian reserve picture?
4. Are there reversible drivers (thyroid, prolactin, insulin, micronutrients)?
5. What's the male partner's workup? (Half the equation. Often skipped.)

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A note on AMH anxiety

A low AMH is upsetting. It is also not a diagnosis of infertility. AMH predicts how you'd respond to IVF stimulation; it does not predict your ability to conceive naturally in any given month.

Some of my patients with very low AMH conceive without intervention. Some patients with reassuring AMH need significant support. Numbers contextualize. They don't decide.

If you'd like a real fertility workup — not just "everything looks normal" — that's a conversation I have often.