High FSH or low AMH: what it means for your fertility

If you are looking into your fertility, you have probably heard of two blood tests: FSH and AMH. These are the two most widely used markers of ovarian reserve — the number of eggs you have left.

Unlike men, who produce sperm throughout their lives, women are born with a fixed number of eggs that declines every month until the menopause. Estimating how many eggs are left is not an academic exercise — it determines what to expect from each IVF attempt and how much time you have.

How the ovarian pool declines with age

From 1-2 million eggs at birth, the number falls to about 400,000 at puberty and continues to drop steadily every month. For one egg to be released through ovulation, roughly 500 others are lost through a process called atresia (natural cell death).

With age, ovarian function declines progressively. Two things happen at the same time: the quantity of eggs falls (how many remain), and the quality begins to fall too (how many carry normal chromosomes).

FSH and AMH: two different windows on the same thing

The two tests measure ovarian reserve from different angles:

FSH (follicle-stimulating hormone): produced by the pituitary gland, FSH tells the ovaries to grow a follicle. When the reserve falls, the body produces more FSH to compensate — so high FSH is an indirect sign of low reserve. The test is done on day 1-3 of the cycle, always together with oestradiol (otherwise it can be misleading).

AMH (anti-Müllerian hormone): produced directly by the small follicles in your ovaries. It is a direct measure of how many small follicles you have. AMH can be tested on any day of the cycle and is unaffected by oestradiol levels. Combined contraceptives matter: they lower AMH by 20-30% while in use, so a reliable measurement requires about 2 months off the pill.

A third, equally important measure is the ultrasound antral follicle count (AFC) in the first days of the cycle — 6-7 follicles per ovary are considered normal.

When is FSH “high” and when is AMH “low”

FSH (day 1-3 of the cycle):

• Normal: under 10 IU/L
• High: 10 to 20 IU/L
• Very high: above 20 IU/L
• Above 25 IU/L: ovarian stimulation usually yields nothing — the ovaries do not respond

AMH:

• Normal: 1.0 to 3.5 ng/ml
• Low: 0.5 to 1.0 ng/ml (reduced reserve)
• Very low: below 0.5 ng/ml (markedly reduced)
• High (above 3.5 ng/ml): usually associated with polycystic ovary syndrome

What this means for pregnancy

High FSH or low AMH is not the problem itself — it is a reflection of the fact that the ovaries hold fewer eggs than expected for your age. In practice this means:

• Fewer eggs per stimulation cycle — even on high drug doses
• Fewer embryos after fertilisation
• Lower pregnancy rates per attempt
• More attempts are often required

Important: high FSH or low AMH does not mean you cannot conceive with your own eggs. It means the chance per attempt is lower and that time matters even more.

What does NOT help — three misconceptions

“If we lower FSH with drugs, things will improve.” No. High FSH is not the problem — it is the reflection of the problem. Suppressing FSH with the pill or GnRH analogues lowers the numbers but does not change the ovarian reserve.

“High doses of gonadotrophins will overcome the problem.” No. When the ovaries do not contain enough small follicles, larger drug doses do not create them.

“Supplements (DHEA, growth hormone, CoQ10) will improve things.” According to current international guidelines, these interventions do not have enough robust evidence to be recommended as routine.

What can be done

Modern classification (POSEIDON): women with reduced ovarian reserve are classified into four groups based on age and prior response. This helps tailor the stimulation protocol.

Stimulation protocols: antagonist protocols are the most flexible. In selected cases, dual stimulation (DuoStim — two stimulations within one cycle) can maximise the number of eggs per month.

Embryo accumulation: multiple retrieval cycles until enough embryos are collected for transfer, typically combined with PGT-A to select euploid embryos.

Egg donation: when IVF with the patient’s own eggs does not lead to pregnancy, donor eggs are the most effective option — pregnancy rates above 50% per transfer, depending on the donor’s age.

Summary: what to remember

• High FSH or low AMH is an early warning — it does not mean pregnancy is impossible.
• Drugs can shift the values temporarily, but they do not change the actual ovarian reserve.
• The woman’s age matters as much as the values — the earlier the evaluation, the more options remain.
• Treatment is adapted accordingly: individualised stimulation protocols based on POSEIDON, embryo accumulation across cycles, or egg donation when appropriate.

Questions for your doctor

• What are my values, and how do they compare to my age?
• Has an AFC (antral follicle count) been performed?
• Which POSEIDON group am I in?
• Which stimulation protocol do you recommend for me?
• How many attempts should I make before we consider alternatives?

FSH and AMH do not change your ovarian reserve — they show us how many eggs remain. The most important thing we can do is not lose time.