What is an antral follicle count (AFC) and why is it performed?

The antral follicle count (AFC) is a non-invasive test used to assess a woman's ovarian reserve - the number of eggs contained in her ovaries at any given time. Because of this, antral follicle counts are routinely performed in fertility studies in reproductive centers.

However, even if a pregnancy is not being sought, the assessment of the ovarian reserve would allow the woman to make reproductive decisions in advance to avoid possible problems when motherhood is desired in the future.

Currently, the AFC and the determination of anti-Müllerian hormone (AMH) are the most widely used methods to evaluate the ovarian reserve of women.

What is the ovarian reserve?

The ovaries have a certain number of eggs at birth, which is reduced throughout the woman's life. At birth, there are approximately 1-2 million immature eggs in the ovaries. However, by puberty, a woman's ovarian reserve will have been reduced to 400,000-500,000 immature eggs.

With the onset of menstrual cycles, the ovary will release a mature egg each month. Despite this, many other oocytes will fail to mature and will be lost in a process known as atresia. In this way, the number of oocytes is progressively reduced until their depletion at menopause, when menstruation disappears.

Decreased ovarian reserve

Therefore, from the age of 35 onwards, women's reproductive capacity begins to decline, which becomes more pronounced from the age of 40 onwards. Eggs are not only reduced in quantity but also in quality, so female fertility decreases with age.

However, although it is very important, age is not the only factor that determines ovarian reserve, as there may be cases of low ovarian reserve in young women. Hence the importance of assessing  the ovarian reserve in time to be able to make reproductive decisions, even if motherhood is not yet desired.

Antral follicles

Antral follicles are ovarian follicles that still contain immature eggs inside. However, these antral follicles are already sensitive to follicle-stimulating hormone (FSH) and are likely to advance in their development to the pre-ovulatory follicles. However, only one of the antral follicles will develop each month and give rise to a mature egg, which will be released from the ovary with ovulation.

Follicular development

Antral follicles are characterized by having a cavity inside, called antrum, in which follicular fluid accumulates. These antral follicles can be visualized on ultrasound when they are 1-2 mm in diameter, which allows them to be counted.

Antral Follicle Count (AFC)

Antral follicle count (AFC) is a method used to assess a woman's ovarian reserve. It is advisable to perform the AFC  at the beginning of the menstrual cycle, between the second and fourth day, in the early follicular phase. This determination of the number of antral follicles is carried out by the gynecologist by means of a transvaginal ultrasound. Therefore, AFC is a non-invasive and painless test for women.

Antral follicle count by transvaginal ultrasound scanning

In general, the antral follicle count is considered normal when 5-10 follicles (2-10 mm) can be counted in each ovary. In this case, the diagnosis based on the RFA would be a normal ovarian reserve.

However, three other situations can occur when performing the RFA:

• Low reserve: the count is less than 5 antral follicles in each ovary.
• High reserve: more than 10-12 follicles are counted in each ovary.
• Polycystic ovaries: more than 12-13 antral follicles larger than 2 mm. The ovary is enlarged and an ultrasound image resembling a string of pearls is seen.

Knowing the state of the ovarian reserve at a young age will allow a woman to make decisions before it is too late to achieve her desire for motherhood. Thus, a young woman with a low fertility reserve could decide not to postpone childbearing any longer or to preserve fertility by vitrification of eggs.

AFC and fertility treatments

On the other hand, within assisted reproduction treatments, the AFC is also a good predictor of how the ovary will respond to the ovarian stimulation performed. This is why AFC is related to the chances of success of in vitro fertilization (IVF) treatments. The explanation is that the higher the antral follicle count, the more oocytes can be expected to be obtained in the ovarian puncture after stimulation. In this way, starting from a good number of oocytes, the chances of success of the reproduction treatment increase.

Therefore, the AFC before carrying out an assisted reproduction treatment will allow the specialist to personalize the dose and the ovarian stimulation protocol to the situation of each patient. This optimizes the chances of success and avoids possible associated risks such as ovarian hyperstimulation syndrome (OHSS).

Video on antral follicle count

Michelle Emblenton, biochemist at inviTRA, summarises in this video what the antral follicle count (AFR) is and what it is used for.

As Michelle comments:

The ovaries have a certain number of eggs at Birth and this is usually around one to two million eggs. A woman is born with all of the eggs she will ever have throughout her life. When a woman reaches puberty the number of eggs will have been reduced to approximately four hundred thousand to five hundred thousand.

FAQs from users

Does age also influence the antral follicle count?

Undoubtedly. Age is the non-modifiable factor most closely related to ovarian reserve. Ovarian reserve is evaluated fundamentally on the basis of two parameters.

On the one hand, the antimüllerian hormone value (a hormone produced by the granulosa cells of the ovary) and, on the other hand, the antral follicle count by ultrasound. Antral follicles are small spheres of fluid content inside the ovaries. The antral follicle count is the transvaginal ultrasound count of all follicular structures measuring between 2 and 10 mm in the first phase of the cycle (ideally between days 3 and 5 of the menstrual cycle).

We know that ovarian reserve is inversely proportional to age. The older the age, the lower the ovarian reserve, and conversely, the younger the woman, the higher the ovarian reserve. Therefore, age directly influences the antral follicle count.

Is AFC a good marker of ovarian reserve?

Antral follicle count is a good marker of ovarian reserve. The number of antral follicles can vary each cycle and its count is very observer-dependent. For this reason, it should be assessed together with the measurement of anti-Müllerian hormone, which is a parameter with less variability.

Ovarian reserve, together with age, are the parameters that best predict the outcome of in vitro fertilization. When the ultrasound shows a normal to high number of antral follicles (more than 8), it can be expected that a good number of eggs will be obtained during ovarian stimulation and that the possibility of pregnancy will be greater. On the contrary, if only a few follicles are observed, the response will be lower and the possibility of pregnancy lower.

Does the AFC establish the likelihood of IVF success?

The AFC or antral follicle count is one of the most widely used markers of ovarian reserve, together with AMH (Antimullerian Hormone). It consists of assessing the number of antral follicles in each of the ovaries by vaginal ultrasound, a normal value being considered to be around 8-12 follicles in total.

In general, ovarian reserve decreases with age, and therefore the AFC, however, not all women of the same age have the same ovarian reserve and it is therefore important to assess it for any assisted reproduction treatment and in patients who are infertile or wish to preserve their fertility.

The AFR can help us to predict the chances of success in IVF, but it is not the only parameter to take into account, since it tells us about quantity, but not oocyte quality.

Oocyte quality is mainly associated with the woman's age, and refers to the possibility of her oocytes giving rise to a healthy embryo with the capacity for evolutionary pregnancy. It has been established that in patients up to 35 years of age, each embryo generated with their oocytes has a 65-70% chance of giving rise to a healthy embryo. This percentage decreases as the years go by, and at 38 years of age we are talking about 30%, at 40 years of age 25% and at 42 or 43 years of age less than 20-10%.

There are also other factors that can have a negative influence on oocyte quality, such as the consumption of toxic substances, concomitant illnesses, ovarian endometriosis, stress and unhealthy lifestyle habits.

Can I have an antral follicle count at any time?

Regarding the timing of the menstrual cycle, the antral follicle count (AFC) is recommended to be done between the second and fourth day of the cycle. It should be noted that day 1 of the menstrual cycle is considered the day on which menses ends.

On the other hand, as for the time in reproductive life, a woman not only can, but should have an AFC at a gynaecological check-up at a young age, even if she is not seeking pregnancy. In this way, the woman will be able to know her ovarian reserve in order to anticipate and avoid possible complications, for example through fertility preservation, if she wishes to become a mother in the future.
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Will I be able to get pregnant if I have a low antral follicle count?

The chances of getting pregnant with a low antral follicle count decrease with age, not only because of the decrease in the quantity of oocytes but also because of the decrease in quality. However, the specialist will be the one to assess each case and estimate the chances of success, and may opt for the reception of donated oocytes as an alternative to seek gestation.

If I have a high antral follicle count will I develop ovarian hyperstimulation syndrome (OHSS)?

No, you don't have to. The antral follicle count prior to ovarian stimulation in IVF treatments will allow the specialist to adjust the stimulation protocol and dose to avoid the occurrence of OHSS. In addition, during ovarian stimulation, serum oestradiol levels are monitored by ultrasound and blood tests, which will allow the gynaecologist to assess how the ovaries are responding to the treatment and to see if the response is being exaggerated.

Recommended reading

If you would like more information, we recommend that you continue your reading with this article: How Many Eggs Does a Woman Have? - Your Egg Count by Age.

If, on the other hand, you are interested in knowing more about the anti-Müllerian hormone, we recommend reading this article: What Is the Function of Anti-Müllerian hormone (AMH)?