Guide to Antral Follicle Count

Key Takeaways

• Follicles develop in groups during the menstrual cycle, but ultimately only one reaches full maturity and releases an egg during each cycle.
• Antral follicles are small, fluid-filled sacs with eggs inside them that grow on the outside of ovaries, eventually rupturing and releasing an egg during ovulation.
• Age is a major determinant of how many follicles grow and become viable in each cycle, but certain medications can stimulate follicles and increase the number reaching maturity at once.

What are Antral follicles?

Antral follicles are small fluid-filled sacs in the ovaries, each with an immature egg called an oocyte that is expected to mature. The mature egg will be released during the menstrual cycle and wait to be fertilized and give a positive pregnancy. 

Antral follicles are formed from birth but their development and maturation happen throughout a woman’s lifetime. During each menstrual cycle, several antral follicles compete to reach maturity but usually, only one will mature and wait for fertilization. The antral follicles, that don’t mature are discarded. The number of antral follicles a woman produces in each cycle is directly proportional to her ovarian reserve. 

The antral follicle count

An antral follicle count focuses on the antral follicles and the number of antral follicles that mature differs among women. Studies comparing the anti-mullerian hormone and the antral follicle count have shown that the antral follicle count is a great fertility indicator for ovarian reserves. 

How To Test The Antral Follicle Count (AFC)

The antral follicle count (AFC) test is done as the antral follicles begin to grow, typically 3 to 5 days into the menstrual cycle.  The test is done using a transvaginal ultrasound scan, which takes a few minutes and gives a clearer picture of the ovaries as well as the number of antral follicles that measure between 2 and 10 mm, as these are the ones most likely to mature and be fertilized.

If the antral follicle count is between 10 and 20 follicles, the ovarian reserve is normal. On the other hand, if the number is less than 10, the ovarian reserve is considered to be low. Using the AFC test, fertility centers like Ivy Fertility can understand an individual’s infertility and provide insight into: 

Ovarian reserve

The AFC test allows specialists to know the number of eggs in a woman’s ovaries at any given time. It even works better when complemented with blood tests to check the levels of follicle stimulating hormone (FSH), oestradiol, anti-Müllerian hormone (AMH), and luteinizing hormone (LH). 

Potential fertility problems

The test can reveal if the antral follicle count is low, which can be a sign of decreased ovarian function. Decreased ovarian function affects fertility and the test helps the doctor to address any potential fertility problems and design a fertility treatment plan, including the approach, timing, and treatment doses.

Whether ovarian stimulation has worked

The antral follicle count can help predict a woman’s response to ovarian stimulation. This is because if the number of antral follicles is low, the response to IVF hormone treatment may also be low, meaning that the treatment may not work as expected. Knowing the AFC will help the doctor determine the right drug protocol. 

What Is a Normal Antral Follicle Count?

The total AFC is the sum of the antral follicles in both ovaries. It’s normal for this count to vary between ovaries, and this is usually no cause for concern as long as the total count is within the normal range. Additionally, what is considered a normal AFC varies between institutions and most people look at a range to determine how high or low the count may be. 

• Below 4: This is an extremely low count and may not respond to ovarian stimulation.
• 4-9: This is also a low count and people with such a count will likely need high doses to stimulate ovaries adequately. 
• 9-21: This is an Intermediate to normal count with low to great response to drug stimulation. Most women fall into this category. 
• 22-35: This is a normal antral count and people with this count should have an excellent response to ovarian stimulation. 
• Over 35: This is a high count. However, doctors watch out for polycystic ovarian syndrome (PCOS) which may have a negative response to ovarian stimulation and result in overstimulation instead.  

Normal Antral Follicle Count by Age:

Age is a key factor when looking at AFC, this is due to the fact that AFC reduces with age. This means that the older one grows the fewer the follicles produced and the lesser the chances of becoming pregnant.  A study conducted on women aged 25-46 years found an average AFC decline of around 5 percent for individuals under the age of 37, with that decline increasing to almost 12 percent in the following years.

• 20-24 years: 12-30 follicles
• 25-34 years: 13-25 follicles
• 35-40 years: 10-15 follicles
• 41-45 years: 3-10 follicles
• 46+ years: 0-3 follicles

Nevertheless, age is not the sole determinant of fertility in a woman and various factors come into play, including overall lifestyle and genetics. 

Antral Follicle Count and Fertility

Though a low AFC indicates a low ovarian reserve, it doesn't mean there’s infertility. The converse can also be true- a high AFC doesn't translate to egg viability. Women with low AFC can conceive naturally or with the help of fertility treatments.

Fertility treatments differ. For intrauterine insemination (IUI) only one healthy follicle is needed for a pregnancy to occur. On the other hand, IVF requires a higher number of follicles because it involves retrieving more eggs. 

Although an IVF round requires these numbers, successful treatments are possible with numbers outside this range. This makes multiple pregnancies a high possibility in IVF as opposed to IUIs. Additionally, any extra eggs can be preserved for future use. 

One study found that information from an AFC can provide valuable insight into possible fertility treatments. It also showed that individuals with moderate to high AFC numbers were more successful in their IVF cycles overall. 

Bottom Line

While the AFC is a great way to assess a woman’s fertility, it’s important to assess each woman or couple based on different factors including genetics and lifestyle. Still, the AFC remains as one of the best ways to assess an individual’s fertility. However, a low AFC does not necessarily mean a healthy pregnancy is impossible. Many women have conceived naturally despite tests indicating a declining AFC.