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Follicle to oocyte index (FOI) calculator

How many follicles gave an egg?

Q: How is this different from FORT?

FORT measures follicles that responded to stimulation. FOI measures eggs actually retrieved against the starting cohort — it covers the whole pathway including retrieval.

Q: Can FOI exceed 100%?

Yes. The baseline scan does not see every follicle, so retrieval can exceed the counted antral follicles.

Q: Which is more useful, FOI or FORT?

They answer different questions. FORT stops at follicle response; FOI covers the whole pathway through to eggs in the dish, including the retrieval itself. Read together they show where in the chain a disappointing cycle actually lost ground.

Eggs retrieved relative to the antral follicles available at baseline. A measure of how efficiently the cohort converted.

Eggs retrieved

Total collected

Antral follicle count

At baseline scan

These are example numbers. Replace them with yours, then press Calculate.

Example answer

79%

50–100%

Within the range described as adequate in the POSEIDON literature.

This is a guide, not a diagnosis. Share the result with your doctor.

Your result on the scale

The ranges this calculator uses. Yours is highlighted.

Your numbers

Everything worked out from what you entered.

Eggs retrieved: 11
Antral follicle count: 14

What each result means

Your result is highlighted. Your own clinic's advice always comes first.

Your result<50%

Suboptimal. Suggests the available cohort did not convert efficiently — a protocol question rather than a reserve question.

Your result50–100%

Within the range described as adequate in the POSEIDON literature.

Your result100%+

More eggs than baseline antral follicles, which happens and reflects follicles not visible at the baseline scan.

Where this fits in your journey

The usual order, from trying to conceive to pregnancy. Not everyone needs every stage. This calculator belongs to stage 4.

Stage 4 · you are here

During an IVF cycle

Make sense of the numbers your clinic gives you.

Medicines
→
Egg collection
→
Your embryos

This calculator: How many follicles gave an egg?

Calculators for what comes next

How this is worked out

Exact calculationArithmetic on the numbers you enter. If your inputs are right, this figure is right.

The follicle to oocyte index is eggs retrieved divided by antral follicle count. Below 50% is used in the POSEIDON framework as a marker of hyporesponse despite adequate reserve.

About this calculator

?What it tells you

Follicle to oocyte index (FOI). Eggs retrieved relative to the antral follicles available at baseline. A measure of how efficiently the cohort converted.

✓When to use it

After retrieval, alongside FORT rather than instead of it

iWhat you need

Eggs retrieved
Antral follicle count

!What it cannot tell you

FOI is a research-derived index used within the POSEIDON framework, not a standalone measure.

Common questions

How is this different from FORT?

FORT measures follicles that responded to stimulation. FOI measures eggs actually retrieved against the starting cohort — it covers the whole pathway including retrieval.

Can FOI exceed 100%?

Yes. The baseline scan does not see every follicle, so retrieval can exceed the counted antral follicles.

Which is more useful, FOI or FORT?

They answer different questions. FORT stops at follicle response; FOI covers the whole pathway through to eggs in the dish, including the retrieval itself. Read together they show where in the chain a disappointing cycle actually lost ground.

Sources

FOI below 50% is used in the POSEIDON framework as a marker of hyporesponse despite adequate reserve.

POSEIDON criteria for low prognosis patients

In an emergency

If you have any of the warning signs listed here, don't wait for a test result or a calculator. Get help now.

112All emergencies, anywhere in India 108Ambulance

Also call your IVF clinic. Most clinics give an emergency number on your treatment or discharge sheet. Save it in your phone now, before you need it.