What Is an Antral Follicle and How Does It Impact Pregnancy?

Fundamental understanding of eggs, follicles, and the menstrual cycle is crucial for women’s reproductive health. This knowledge can significantly enhance personal well-being and help prevent various fertility-related issues. So, what exactly is an antral follicle, and how does it influence women's pregnancy? In this article, we will delve into the vital role of antral follicles in ovarian function and fertility, providing insights into how their count and health can affect a woman’s chances of conception. Join us as we explore this important topic in detail.

What Are Follicles?

A follicle is a small, sac-like structure that produces or holds a specific cell or substance. Follicles are found in several organs, including the skin (hair follicles), the thyroid gland, and the lymph nodes. In the ovaries, follicles are fluid-filled sacs, also called egg sacs, and each contains an immature egg. They nourish the egg and release hormones that regulate the menstrual cycle. This is why follicles are central to fertility assessment.

What Is an Ovarian Follicle?

An ovarian follicle is a fluid-filled sac in the ovary that holds one immature egg (oocyte). It nourishes the egg and produces hormones, such as estrogen, that regulate the menstrual cycle.

Each cycle, a group of follicles begins to grow, but usually only one becomes dominant and releases its egg at ovulation. The rest break down and are reabsorbed, a process called atresia. Over 99% of ovarian follicles never ovulate.

What Is an Antral Follicle?

An antral follicle is a small, growing follicle that has formed a fluid-filled cavity called an antrum. It measures about 2 to 10 mm, which makes it visible on ultrasound.

A girl is born with roughly one to two million follicles, most of them dormant and too small to see. Over several months, some are activated and grow, and those that form an antrum become countable. Doctors use them to assess ovarian health:

• Antral follicle count (AFC): a transvaginal ultrasound early in the cycle counts the antral follicles in both ovaries. This estimates ovarian reserve and helps predict the response to ovarian stimulation in IVF.
• AMH: small growing follicles, including antral ones, produce anti-Müllerian hormone. The blood level of AMH is another marker of ovarian reserve.
• Low count: a consistently low AFC suggests diminished ovarian reserve.
• High count: a very high AFC, often 20 or more per ovary, can be one feature of polycystic ovary syndrome (PCOS), which is diagnosed alongside other criteria.

The count falls naturally with age. It reflects the quantity of eggs, not their quality, so a fertility specialist interprets it together with age, hormone tests, and medical history.

What Is the Antrum in an Ovarian Follicle?

The antrum is a fluid-filled cavity (antral cavity) that forms inside a growing ovarian follicle. It appears when the follicle moves from the preantral to the antral stage, and it is filled with follicular fluid containing hormones and nutrients that support the egg. The antrum is one of the features that makes a follicle visible on ultrasound, which is why doctors can count antral follicles during a fertility assessment.

Why Are Follicles Important?

Ovarian follicles play a crucial role in women's reproductive health. They also perform the following essential functions in the body:

• Secreting hormones that regulate the menstrual cycle.
• Nourishing eggs until they are ready for ovulation.
• Protecting immature eggs.

What Is a Normal Number of Antral Follicles?

There is no single universal normal range, but an antral follicle count (AFC) of about 7 to 15 follicles (2 to 10 mm) across both ovaries is generally considered average, fewer than 5 to 7 is considered low, and more than about 15 is considered high. The count falls with age and depends on the ultrasound equipment and operator. It reflects egg quantity, not quality, so a low AFC does not mean infertility, and a specialist interprets it together with age and AMH. 

Antral Follicles and Ovarian Reserve

As mentioned earlier, antral follicles in the ovaries are small before they grow and release an egg, typically measuring around 2 to 9 millimeters in diameter. The antral follicle count (AFC) can be determined via ultrasound, which also indicates the number of remaining eggs in the ovaries.

The higher the number of antral follicles in the ovaries, the greater the chances of natural conception. Additionally, for women considering pregnancy through IVF, the antral follicle count plays a crucial role in determining the likelihood of IVF success.

How Do Antral Follicles Determine Fertility?

As mentioned earlier, the more antral follicles present in the body (as long as the count remains within a normal range), the higher the likelihood of natural conception. Each day, primary follicles are activated by hormonal signals and begin their growth process.

These follicles continue to grow, increasing in size. As noted earlier, some of these follicles disintegrate before reaching the third stage (antrum formation), while others absorb this fluid and develop into antral follicles. These follicles typically measure between 2 to 10 millimeters in diameter. A woman's fertility is assessed by considering the number of antral follicles along with other factors.

Read more: The First Step in Infertility Treatment: Where Should I Start

What Is the AFC Test or Antral Follicle Count?

The Antral Follicle Count (AFC) test is a fertility assessment performed via transvaginal ultrasound. This test is usually conducted between the second and fifth days of the menstrual cycle. During the procedure, the ultrasound technician examines each ovary and identifies follicles measuring between 2 to 10 millimeters in diameter. In addition to assessing fertility, antral follicle count can also be prescribed for the following purposes:

Initial diagnosis of ovarian issues

• Evaluation of ovarian function
• Determining fertility based on age
• Assisting in the diagnosis of polycystic ovary syndrome (PCOS)

Is Antral Follicle Count Used to Diagnose PCOS?

Antral follicle count is one of the tools doctors use to evaluate polycystic ovary syndrome (PCOS), but it is never the only criterion. A high count, commonly 20 or more follicles (2 to 9 mm) in at least one ovary on a high-resolution transvaginal ultrasound, supports the diagnosis when combined with irregular ovulation and signs of high androgen levels. A gynecologist or fertility specialist interprets the result together with symptoms and blood tests, including AMH.

Read more: How to Cure PCOS to Get Pregnant?

Determining the Normal Antral Follicle Count in the Ovaries

In the previous section, we discussed the approximate normal count of antral follicles in the body. But how did doctors establish this baseline? A classic study was conducted on women with confirmed fertility to determine the normal range of antral follicles. The women participating in this study had to meet the following specific criteria:

• They had a regular menstrual cycle, typically ranging from 21 to 35 days.
• They had given birth to at least one child in the past.
• They had stopped using birth control pills at least two months prior.
• They were ovulating, which was confirmed by measuring their basal body temperature.
• They did not have any hormonal or reproductive organ-related diseases.

How to Diagnose Diseases Affecting Ovarian Follicles؟

As mentioned earlier, issues related to ovarian follicles are not limited to their count but can also lead to other complications in the body. The following diagnostic and therapeutic methods can be used to identify these complications:

• Blood Tests
• Blood tests are used to measure hormone levels in the body.
• Pelvic Ultrasound
• This ultrasound allows doctors to examine the size of the ovaries and the number of antral follicles.
• Laparoscopy
• Laparoscopy is a surgical procedure performed under anesthesia. In this method, the doctor inserts a tool into the body to examine the ovaries and check for possible cysts.

Antral Follicle Diagnostic Procedures in Iran 

Iran has emerged as a leading destination for advanced fertility treatments and diagnostic procedures, including assessments of antral follicles. The country boasts world-class medical facilities, highly skilled specialists, and competitive healthcare costs. RaadinaHealth, a prominent health tourism agency, offers comprehensive support for those traveling to Iran for medical care. They provide tailored packages that include the best offers for clinics, comfortable hotels for your stay, seamless transfers, and expert consultations. By choosing RaadinaHealth, patients can ensure a smooth and stress-free journey while receiving top-notch medical services in a country renowned for its commitment to healthcare excellence.

Conclusion

The antral follicle count is one of the most useful markers of ovarian reserve. Together with AMH and age, it helps a fertility specialist plan treatment, including the ovarian stimulation protocol in IVF. It reflects egg quantity rather than quality, so the result is always interpreted in the context of your full medical history.

If you are considering an AFC test or fertility evaluation in Iran, RaadinaHealth can guide you through the process. Our team helps you choose a suitable clinic and fertility specialist, arranges your consultation, and organizes your hotel and transfers. 

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FAQs

How is the antral follicle count (AFC) determined?

The AFC is typically assessed through a transvaginal ultrasound performed between the second and fifth days of the menstrual cycle. The technician counts the visible antral follicles measuring 2 to 10 millimeters in diameter.

What is considered a normal antral follicle count?

A normal antral follicle count can vary by age. Generally, having more than four antral follicles is considered normal for women of reproductive age. Women planning for IVF should aim for around 20 follicles.

How do antral follicles affect fertility?

The number of antral follicles is an important indicator of ovarian reserve, which directly impacts a woman’s fertility. A higher count typically increases the chances of natural conception and the success rate of fertility treatments like IVF.

What factors can influence the antral follicle count?

Several factors can affect the antral follicle count, including age, hormonal balance, and underlying health conditions such as polycystic ovary syndrome (PCOS) or ovarian insufficiency.

Can a low antral follicle count indicate infertility?

While a low antral follicle count may indicate a reduced ovarian reserve and can lower the chances of conception, it does not necessarily mean infertility. Many women with low counts can still conceive naturally or with assisted reproductive technologies.

How can I get tested for antral follicles in Iran?

You can receive comprehensive fertility assessments, including antral follicle count tests, through various medical facilities in Iran. Agencies like RaadinaHealth can assist in arranging your medical travel, including consultations and diagnostic procedures.

What is the relationship between antral follicles and ovarian reserve?

Antral follicles serve as an indicator of a woman’s ovarian reserve, which refers to the number of viable eggs available in the ovaries. A higher count of antral follicles typically suggests a better ovarian reserve, which is important for fertility.

How often should women monitor their antral follicle count?

Routine monitoring of the antral follicle count is generally not necessary for all women. However, those facing fertility issues or considering assisted reproductive technologies may benefit from regular assessments, typically conducted by a fertility specialist.

Can lifestyle factors affect antral follicle health?

Yes, lifestyle factors such as diet, exercise, smoking, and alcohol consumption can influence ovarian health and the antral follicle count. Maintaining a healthy lifestyle can positively impact reproductive health and fertility.

What are the signs of ovarian issues related to antral follicles?

Signs of potential ovarian issues may include irregular menstrual cycles, difficulty conceiving, and symptoms associated with hormonal imbalances, such as excessive hair growth or acne. If these symptoms occur, it is advisable to consult a healthcare professional.

Are there treatments available for low antral follicle counts?

While there is no specific treatment to increase antral follicle counts, fertility treatments such as ovarian stimulation protocols during IVF may help maximize the chances of success for women with lower counts. Consulting a fertility specialist can provide personalized recommendations.

How can I prepare for an antral follicle count test?

To prepare for an antral follicle count test, it’s recommended to have the ultrasound scheduled between the second and fifth days of your menstrual cycle. It’s also important to inform your healthcare provider of any medications you are taking, especially hormonal treatments.