Antral follicle count on ultrasound: how many is normal and what “low” or “high” means
In short: antral follicles are small follicles of 2–10 mm that are visible in the ovaries at the start of the cycle. They are counted on ultrasound on cycle days 2–5, and the total for both ovaries is usually 10–20. Fewer than 5–7 points to a reduced egg supply; twenty or more in one ovary is a polycystic picture. Neither is a diagnosis in itself. Here is how I count them, what the numbers mean and when something really needs to be done about them.
What antral follicles are
In every cycle the ovaries line up a group of small follicles. At the start of the cycle they show on the screen as dark round bubbles of 2–10 mm — these are the antral follicles. Within a few days one of them pulls ahead and becomes the dominant follicle, and the rest fade away.
They are worth counting because the number of antral follicles reflects the egg supply — what is called the ovarian reserve. In a report it appears as “AFC” (antral follicle count), with a number for each ovary.
Which day and how they are counted
- On cycle days 2–5, before a large follicle or a corpus luteum appears: later the small follicles are harder to see and the count comes out too low.
- With a transvaginal probe — follicles of 2–3 mm simply cannot be seen through the abdomen.
- In both ovaries, every follicle from 2 to 10 mm; the result is the total. For the reserve, follicles of 2–10 mm are counted; for a polycystic picture, 2–9 mm.
Two caveats explain most needless worry. On hormonal contraception fewer follicles are visible than are really there: the count recovers after stopping, so the reserve is better assessed two to three months later. And the number shifts by a few from cycle to cycle — that is normal variation, not “the reserve dropped in a month”.
No separate service is needed: the count is part of an ordinary pelvic ultrasound, as long as you come at the start of the cycle and say the reserve is what you want checked. How to prepare is covered in the article on pelvic ultrasound.
How many follicles is normal
| Total in both ovaries | How it is read |
|---|---|
| fewer than 5–7 | reduced ovarian reserve |
| 7–9 | below average; at 38–40 this is the usual picture |
| 10–20 | an ordinary supply at 25–35 |
| more than 20 | a high reserve; often multifollicular ovaries |
| 20 or more in one ovary (or a volume of 10 ml or more) | a polycystic picture — not a diagnosis, but a reason to look at the cycle and hormones |
Authors differ by a follicle or two on the cut-offs, so a single “9” or “11” settles nothing. Age matters more: the number of follicles falls over the years, and eight at 41 is expected, while eight at 27 is a reason to look into it.
When the count is low
A low count describes the number of eggs, not their quality and not whether pregnancy will happen. With a regular ovulatory cycle, women with a low reserve conceive naturally about as often as women of the same age with a high one: reserve tests do not predict this.
What a low count really changes:
- timing — if pregnancy is in your plans, it is not worth putting it off for years;
- the approach to infertility — the reserve determines how the ovaries respond to stimulation, and that is taken into account when a method is chosen;
- the scope of testing — AMH and FSH are added to the scan, so that nothing rests on a single marker.
What is not needed is “ovary vitamins” or hormones for the sake of the number: the supply cannot be increased, it is set at birth. What to check before pregnancy is covered separately.
When it is high: multifollicular ovaries and PCOS
Three different phrases turn up in reports here, and they are constantly confused.
- Multifollicular ovaries — more follicles than usual, but an ovary of normal size. A common normal variant in young women, after stopping contraception, under stress and after rapid weight loss. It needs no treatment.
- A polycystic picture — 20 or more follicles in one ovary, or an ovarian volume of 10 ml or more. The older criteria used a threshold of 12, and it still appears in reports. This describes the image, not a disease: the same picture is found in healthy women.
- Polycystic ovary syndrome (PCOS) — a diagnosis that needs two features out of three: infrequent or absent ovulation, signs of excess androgens (acne, hair growth, blood tests) and a polycystic picture on ultrasound (in adults, a raised AMH can be used instead) — provided other causes (thyroid, prolactin, adrenal glands) have been ruled out. A scan alone is not enough.
Two practical conclusions follow. If the cycle is regular and there are no symptoms, “many follicles” simply means a good reserve. And in teenagers ultrasound is not used as a criterion: the diagnosis rests on the cycle and signs of excess androgens, because for the first eight years after the first period almost everyone’s ovaries look “multifollicular”.
How a polycystic picture differs from cysts, and what else can be seen in the ovaries on ultrasound, is covered in the article on ovarian ultrasound.
What to do with the result
I do not draw conclusions from a single count. If the number stands out, the order is this:
- count again in the next cycle, on days 2–5, off hormonal medication;
- add blood tests — AMH on any cycle day, FSH and estradiol on days 2–4; androgens if PCOS is suspected;
- check whether ovulation happens — that is folliculometry, two to four short visits in a cycle; how it works is explained in the article on folliculometry.
Do not put off a visit if pregnancy has not happened after a year of regular intercourse, or after six months if you are over 35: that is where infertility testing starts, and the follicle count is one of its first steps.
I do the ultrasound myself and hold a PTGiP certificate. I see patients at ul. Głębocka 9/U1 in Warsaw; a pelvic ultrasound is 250 zł, and no referral or insurance is needed. Appointments are not held in English — bring someone who can interpret, or tell me in advance. If you have earlier reports, bring them: the trend says more than a single number.
In brief, as questions
How many antral follicles is normal?
At 25–35 the total for both ovaries is usually 10–20. Fewer than 5–7 is regarded as a reduced reserve, and 20 or more in one ovary as a polycystic picture. The number falls with age, so it is always read together with age.
On which cycle day are antral follicles counted?
On cycle days 2–5, with a transvaginal probe. Later a large follicle and a corpus luteum appear, the small follicles are harder to see and the count comes out too low.
Does a low antral follicle count mean I will not get pregnant?
No. A low count describes the number of eggs, not the chance of pregnancy: with regular ovulation it happens as often as in women of the same age. With a low reserve, though, it is not worth putting pregnancy off for years.
Are multifollicular ovaries the same as PCOS?
No. Multifollicular ovaries are a normal variant: many follicles, but an ovary of normal size. A PCOS diagnosis needs two features out of three: infrequent ovulation, excess androgens and a polycystic picture on ultrasound (in adults, or a raised AMH), and only once other causes have been ruled out.
Can the antral follicle count be increased?
No, the egg supply is set at birth and only declines. Vitamins and hormones do not increase it. The count can look lower on hormonal contraception — it recovers within two to three months of stopping.
Sources
The primary sources this text rests on. Links open in a new tab.
- International evidence-based guideline for the assessment and management of polycystic ovary syndrome (2023)ESHRE — the international guideline: how many follicles count as a polycystic picture and why the picture alone is not a diagnosis
- Testing and interpreting measures of ovarian reserve: a committee opinionASRM, USA — what the follicle count and AMH show, and what they cannot predict
- Polyendocrine metabolic ovarian syndrome (PMOS)NHS, UK — the symptoms of the syndrome and its new name: PMOS, formerly PCOS
- Rekomendacje Polskiego Towarzystwa Ginekologów i PołożnikówPTGiP — the Polish standard of care; the same society issued my ultrasound and colposcopy certificates
This text describes the general picture and does not replace a consultation. Timings and indications differ from woman to woman and are decided at the appointment, from your history and test results.