AMH vs FSH: Which Fertility Hormone Test Matters More?

Author: Dr Lauren, Clinical Lead – Marylebone Diagnostic Centre

Patients are often told conflicting things about fertility hormones. Some are told AMH is everything. Others are told FSH matters more. In reality, AMH and FSH measure very different things, and neither should be interpreted alone. This article explains how these hormones work, how they are used clinically, and why combined testing provides the clearest fertility insight.

What Does the AMH Test Measure?

AMH (Anti-Müllerian Hormone) is produced by small follicles in the ovaries. Clinically, AMH is used to:

• Estimate ovarian reserve
• Predict ovarian response to stimulation
• Support IVF and egg-freezing planning

AMH is relatively stable throughout the cycle and can be tested on any day. However, AMH does not measure:

• Egg quality
• Ovulation
• Chance of natural pregnancy

What Does the FSH Test Measure?

FSH (Follicle-Stimulating Hormone) is released by the pituitary gland. FSH reflects how hard the body is working to stimulate the ovaries. Clinically, FSH helps assess:

• Ovarian responsiveness
• Hormonal signalling between brain and ovaries
• Menstrual cycle regulation

FSH must usually be tested on day 2–3 of the cycle and alongside oestradiol. Unlike AMH, FSH fluctuates significantly.

AMH vs FSH: Key Differences

AMH and FSH answer different clinical questions:

• AMH focuses on: Egg quantity, long-term reserve
• FSH focuses on: Hormonal demand, current ovarian response

A normal FSH does not guarantee good ovarian reserve. A low AMH does not mean pregnancy is impossible. This is why fertility decisions should never rely on one hormone alone.

Which Test Is More Important?

Neither test is “more important”. They are complementary. Clinicians use:

• AMH: To understand reserve and planning
• FSH: To understand cycle dynamics and stimulation response

At MDC, we routinely interpret both together.

Why AMH Alone Can Be Misleading

AMH is frequently over-marketed as a definitive fertility test. Problems arise when:

• Results are reported without explanation
• Patients compare numbers online
• Age and symptoms are ignored

A low AMH can still coexist with regular ovulation and natural conception. Context is everything.

Why FSH Alone Is Also Insufficient

FSH levels can appear normal even when ovarian reserve is reduced. FSH is influenced by:

• Cycle timing
• Oestradiol levels
• Short-term hormonal feedback

This is why FSH must always be interpreted carefully and in combination.

When AMH and FSH Are Used Together

Using both hormones allows clinicians to:

• Assess ovarian reserve
• Understand hormonal effort
• Plan IVF protocols
• Estimate response to stimulation

This combined approach leads to better clinical decisions.

AMH, FSH, and PCOS

In PCOS:

• AMH is often high
• FSH may be normal or low

This pattern reflects increased follicle number and disrupted ovulation. AMH alone may overestimate fertility potential in PCOS, and FSH alone may miss ovulatory dysfunction. Combined testing is essential.

AMH, FSH, and Age

Age changes how results are interpreted. For example:

• A low AMH at 25 has a different meaning than at 40
• A borderline FSH at 35 may require closer monitoring

At MDC, age-adjusted interpretation is standard practice.