Ultrasound Test
Antral Follicle Count (AFC)
A detailed guide to the Antral Follicle Count test: what it measures, how it is performed, and what the results mean for IVF planning and ovarian reserve assessment.
Test Overview
The AFC is a real-time ultrasound measurement of small resting follicles visible in both ovaries at the start of the menstrual cycle. Each antral follicle contains an immature egg and represents the pool available to respond to stimulation.
Key Timing
Performed on Day 2, 3, or 4 of the menstrual cycle, before FSH triggers active follicle growth. A transvaginal ultrasound probe is used for direct ovarian visualization.
1. Purpose and uses of the AFC test
The AFC is one of the two most clinically useful ovarian reserve markers, alongside AMH. Because it is imaging-based rather than hormonal, it captures reserve from a different angle and complements blood test findings.
Clinical uses
- Quantify ovarian reserve: the number of antral follicles directly reflects the size of the remaining primordial follicle pool.
- Predict IVF stimulation response: AFC is the primary tool fertility specialists use to determine starting gonadotropin doses.
- Identify PCOS: a follicle count of 20 or more in either ovary is one of the three Rotterdam diagnostic criteria for polycystic ovary syndrome.
- Assess ovarian aging: AFC declines predictably with age and correlates closely with AMH.
- Guide protocol selection: poor responders (low AFC) and high responders (high AFC) require different IVF medication strategies.
2. Procedure and what to expect
The AFC is performed using transvaginal ultrasound. A narrow probe is inserted into the vagina, allowing the sonographer to view each ovary directly. The procedure takes 10 to 15 minutes and is not considered a surgical test.
What is counted
The sonographer counts all follicles measuring 2 to 10 mm in diameter across both ovaries. Follicles smaller than 2 mm are too immature to identify reliably; follicles larger than 10 mm have already begun responding to FSH and are not part of the resting cohort.
Cycle day matters
Testing outside the early follicular window (Days 2 to 4) reduces accuracy. By Day 5 or 6, some follicles are already becoming dominant and will be excluded from the count, artificially lowering the result.
3. AFC and ovarian reserve
Women are born with a fixed number of primordial follicles. This pool decreases continuously from birth, with a sharper decline after age 35. Antral follicles are the stage just before a follicle becomes responsive to FSH. Counting them gives a snapshot of what is available for a given cycle.
AFC and AMH: different windows on the same reserve
AMH is secreted by the granulosa cells surrounding antral and preantral follicles and reflects the same cohort that AFC counts physically. The two tests correlate strongly, but AFC can vary between cycles by 2 to 4 follicles depending on the sonographer, equipment, and cycle timing. AMH is more stable across cycles. Using both together gives a more complete picture of reserve than either alone.
AFC does not measure egg quality
A high AFC confirms there are eggs available. It does not confirm those eggs are chromosomally normal. Age remains the primary determinant of egg quality.
4. Normal AFC ranges by age
The following ranges are general population averages. Clinics may use slightly different thresholds depending on their patient population and stimulation protocols.
| Age group | Average AFC | IVF response prediction | Clinical category |
|---|---|---|---|
| Under 30 | 15 to 30 | Normal to high | Good reserve |
| 30 to 35 | 12 to 20 | Normal | Adequate reserve |
| 35 to 38 | 8 to 15 | Normal to reduced | Borderline reserve |
| 38 to 42 | 5 to 12 | Reduced | Diminished reserve |
| Over 42 | 3 to 8 | Poor | Low reserve |
| Any age | Below 3 to 4 | Very poor; high cancellation risk | Severely diminished |
5. Interpreting your results
Low AFC (below 5 to 7)
A low count suggests fewer follicles are available to respond to stimulation. This typically results in fewer eggs retrieved during IVF and may increase the likelihood of a cycle being cancelled if the ovaries do not respond adequately to medication.
A low AFC at a younger age is more unexpected than at 40 and warrants further investigation alongside AMH and FSH testing.
High AFC (above 20 to 25 in either ovary)
A high follicle count combined with irregular cycles and other features may support a diagnosis of PCOS. In an IVF context, a high AFC increases the risk of ovarian hyperstimulation syndrome (OHSS), where the ovaries overrespond to stimulation medications. Protocols are adjusted to lower this risk.
Normal fluctuation between cycles
AFC can shift by 2 to 4 follicles between consecutive cycles in the same person. A single count should not be used in isolation to make a final assessment of reserve. Two measurements taken in separate cycles, alongside AMH, provide a more reliable picture.
6. AFC and IVF protocol planning
AFC is the primary input for calculating the starting dose of follicle-stimulating medications (gonadotropins) in IVF. The goal is to stimulate the ovaries enough to retrieve a useful number of eggs without triggering OHSS.
| AFC result | Response category | Typical starting dose | Protocol consideration |
|---|---|---|---|
| Below 5 | Poor responder | 300 to 450 IU/day | May use adjuncts (e.g., growth hormone) |
| 5 to 10 | Low-normal | 225 to 300 IU/day | Close monitoring; antagonist protocol common |
| 11 to 20 | Normal responder | 150 to 225 IU/day | Standard long or antagonist protocol |
| Above 20 | High responder / PCOS | 75 to 150 IU/day | GnRH agonist trigger; freeze-all considered |
Clinics use AFC alongside AMH to finalize protocol decisions. Neither test alone should determine treatment planning.