Antral follicle count

The antral follicle count, usually shortened to AFC, is an ultrasound tally of the small resting follicles visible on both ovaries early in the cycle. It answers the same question as an AMH blood test, from a different angle, and the two are normally read together.

Where you'll meet it

It happens at a transvaginal scan during ovarian reserve testing, often at the same appointment that checks the uterus. You may not be told a count at the time. It appears later in the letter, next to your AMH, and the two of them decide the drug dose for an IVF or egg freezing cycle.

What is being counted

An antral follicle is a small fluid-filled sac holding an immature egg, big enough to see on a scan but not yet growing towards ovulation. The sonographer counts the ones roughly between two and ten millimetres across, on each ovary, and adds them together.

The timing matters. The count is done in the first few days after a period starts, when the follicles are still small and evenly sized and nothing has begun to dominate the cohort. Later in the cycle a lead follicle has taken over and the picture is no longer a fair snapshot of the pool.

It is a straightforward scan, ten to fifteen minutes, uncomfortable rather than painful for most people. A slim probe gives a far clearer view of the ovaries than a scan through the abdomen does.

How it compares with AMH

They measure the same underlying thing. AMH samples the hormone those follicles release into the blood, and the antral count looks at them directly. Where the two disagree, it is usually a sign that one of them caught an off day, which is exactly why clinics like having both.

The count has one weakness the blood test does not. It depends on who is holding the probe and how good the view is. Body habitus, ovaries sitting awkwardly, and the sonographer's own counting habits all move the number. A count from one clinic is not perfectly comparable with a count from another.

What the number is good for

It predicts how many eggs a stimulated cycle is likely to produce, and that is its real job. A high count warns of a strong response and a higher risk of overstimulation. A low count warns of a thin harvest and is a reason to talk about how many cycles the plan should allow for, particularly before freezing eggs, where the number banked is the whole point.

What it does not do is measure egg quality or tell you whether you can conceive without help. That remains driven by age. A reserve test describes the size of the queue, not who is in it.

Questions to ask

Ask what your count was and on which day of the cycle it was taken, and write it down, because it travels with you to any clinic and stops you paying twice. Ask how it reads alongside your AMH and whether the two agree. If they do not, ask which one the plan is being built on and why.

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