HomeFertility WorkupHow Ovarian and Antral Follicles Relate to Fertility

How Ovarian and Antral Follicles Relate to Fertility


An ovarian follicle, also known as an oocyte or immature egg, is a fluid-filled sac found in the ovaries that are a part of the female reproductive system. Every month a mature egg is discharged from a follicle during the process of ovulation. Each cycle, many follicles start to mature, but only one will typically ovulate as an egg (rarely, more than one egg is released, increasing the potential for twins). The follicle develops into a corpus luteum following ovulation.

At any stage of follicular development, the ovarian and antral follicles that do not deliver a mature egg undergo a process known as atresia in which they disintegrate. Ovarian follicles will dissolve in about 99% of cases and never mature sufficiently to deliver an egg. 

During fertility treatments, the growth and development of ovarian and antral follicles are monitored. The purpose of superovulation, which is done during IVF treatment, is to encourage the ovaries to produce several mature follicles simultaneously. An antral follicle count (AFC), commonly known as an ultrasound exam, could be carried out as a part of fertility testing. This examination is performed to gauge ovarian reserves.

What Are Antral Follicles And Their Significance?

The number of AFC in the ovary may theoretically give you an estimate of how many eggs you still have if you knew how many of them there are. Because they are too small to see, it is impossible to count the number of follicles in the ovaries. But once a follicle reaches a specific stage, ultrasonography can detect it.

Follicles begin with very, very little growth. Primordial follicles are the precursors of all AFC in the ovary. It only measures 25 micrometers, or 0.025 millimeters, to be a primordial follicle. With the naked eye alone, let alone on an ultrasound, it is impossible to see. Every day, hormonal cues cause primordial follicles to “wake up” and begin to develop. They get bigger and bigger as long as they keep advancing to the next stage and surviving.

The tertiary stage is one of the stages. The follicle develops a chamber filled with fluid at this period which is known as the antrum. Antral follicles are follicles with an antrum, and they range in size from 2 to 10 mm.

To put things in perspective, a 5 mm long antral follicle is 200 times larger than it was as a primordial follicle. With ultrasound, antrum follicles are evident. According to research, the number of active antral follicles in the ovaries correlates with the number of remaining eggs that may be viable. Even while it’s still unknown how many follicles there are in total, ovarian reserves are probably low if there aren’t many antral follicles growing on the ovaries.

Anti-mullerian hormone (AMH), which is a hormone that circulates in the blood, is produced in greater quantities by antral follicles. Another method to assess ovarian reserves is to measure AMH levels using blood tests. Contrary to FSH and oestrogen (most accurate on day 2 of the cycle) ( AMH levels can be drawn at any time of the cycle).

The Antral Follicle Count  (AFC) Test

Occasionally between cycle days 2 and 5, a transvaginal ultrasound is used to perform an antral follicle count. As part of a fertility evaluation, the test could be performed. Or, it could be requested before a cycle of in vitro fertilization. The ultrasound technologist counts the number of follicles measuring between 2 and 10 mm while examining each ovary during this examination. 

This examination may be recommended by your doctor for the following reasons:

  • Specify your ovarian reserves.
  • Determine the presence of primary ovarian insufficiency.
  • assist in identifying polycystic ovarian syndrome
  • Find out how fertile you are in proportion to your age (whether you have more, less, or about the same number of follicles compared to others your age)

What Is A Normal AFC Count By Age?

Your ovarian reserves will naturally decline as you get older. Therefore, what is a typical normal AFC count for a 25-year-old may not be a typical normal AFC count by age for a 38-year-old. Nevertheless, a count of 3 to 6 antral follicles is regarded as modest or a normal AFC count.

Antral follicle counts were done in a study on women who had been shown to be fertile (most studies on AFC are done on infertile women) 

The women had to meet the following criteria in order to be considered for this study:

  • Have normal menstrual periods that last between 21 and 35 days.
  • Be ovulating, which can be determined by a rise in temperature on a basal body temperature chart.
  • Have at least one child from a previous relationship, born within the last 12 months
  • possess no known hormonal or endocrine disorders
  • Have Stopped taking birth control at least two months prior to the study

Here’s a chart to show the average antral follicle counts (AFC), along with the ranges observed (from the highest AFC count lowest AFC count).

Age range Average AFC Lowest AFC Highest AFC
25 to 34 15 3 30
35 to 40 9 1 25
41 to 46 4 1 17


Low ovarian reserve may not necessarily exclude pregnancy. However, it does imply that you could not experience the same level of success with reproductive treatments as a woman with more adequate ovarian reserves. Results may vary depending on the ultrasound technician’s expertise and the actual ultrasound machine. Consider seeking a second opinion if a test yields subpar results.

Primary ovarian insufficiency, often known as premature ovarian failure, may be identified in women with a very low antral follicle count before the age of 40.  As a woman ages, her natural and antral follicle count declines. A high antral follicle count could be a sign of polycystic ovarian syndrome (PCOS).

Menstrual Cycle And The Role Follicles Play

The follicular phase and the luteal phase are the two main phases of your menstrual cycle. The recruitment of follicles in the tertiary stage of development and the start of the process that will ultimately result in ovulation happen during the follicular stage.

Despite the fact that multiple follicles begin this race, only one (or two) will mature fully and deliver an egg. The ovulatory stage may be reached by a number of follicles if you are on fertility medications. The actual follicles are in charge of:

  • Safeguarding and nourishing the oocyte throughout oogenesis
  • releasing vital hormones for reproduction
  • Following ovulation, changing into the corpus luteum, which releases the hormone progesterone (vital to keep the uterine lining thick and lush for a pregnancy to implant)

The Menstrual Cycle And Follicular Phase

On the first day of your period, the follicular phase of your cycle starts. The body releases the top layer of endometrial tissue during menstruation, which was accumulated in preparation for pregnancy. The uterine lining will be thin after your period. After ovulation, the lining will thicken and expand once more.

But before that happens, during your period, your ovaries are getting ready to ovulate the following egg. In your ovary, five to six follicles will begin to develop. The pituitary gland produces and secretes the hormone known as FSH or follicle-stimulating hormone. This hormone causes the follicles to begin maturing.

The follicles produce more oestrogen as they grow larger. Higher oestrogen levels instruct the pituitary to reduce FSH production. Even if you had five or six follicles when you first started, only one (and perhaps two) will mature. Smaller follicles grow more slowly or even stop growing when FSH levels are low, whereas the larger follicles continue to grow steadily.

One follicle eventually takes over as the dominant one, while the others cease developing and fall apart. Even more, estrogen is released by the follicle when it is almost at its largest size. LH, or luteinizing hormone, is produced and released by the pituitary gland in response to extremely high amounts of estrogen. The follicle is pushed to finish its last stages of development as a result.

Stages of Follicular Development – Folliculogenesis

Contrary to popular belief, follicular development does not begin and terminate during the follicular phase of the menstrual cycle. Before a person is even born, when the ovaries are first developing in a developing fetus, the whole follicular life cycle begins.

The ovaries only have primordial follicles at this stage. Up to 50 years can pass while follicles are in this “sleeping” state before they awaken and begin to go through the phases of development. A primordial follicle develops into a mature, ovulation-ready follicle over the course of six to a year.

Numerous follicles stop growing and die at every stage of follicular development. Every primordial follicle won’t progress through all of the stages. Consider it a race to qualify for the ovulation Olympics. There will be some follicles that fall out and some that grow. Only 1% of women ever ovulate an oocyte. There are three stages of folliculogenesis:

Primordial follicle: All follicles in a newborn baby’s ovaries are in the stage known as the primordial follicle.

Primary follicles: Starting in puberty and continuing until menopause, a small number of primordial follicles transition into the primary follicle stage each day.

Secondary follicles: Theca cells are added, resulting in secondary follicles, and they will produce hormones.

Tertiary follicles: Antral follicles, also referred to as tertiary follicles. Transvaginal ultrasound can detect follicles at this stage, which have a cavity filled with fluid called the antrum.

Graafian follicle: A follicle that is large enough to ovulate; only one or two tertiary follicles will develop into ovulation during each cycle.

Corpus luteum: arises from the open follicle that delivered an egg but is no longer a follicle.

Size of Follicles

Your doctor may use ultrasound to track the development of follicles if you are undergoing fertility treatment. The number of growing follicles will be counted during these ultrasounds. They’ll be measured as well.

Follicle Size

If you have decided to undergo a thorough fertility treatment, your doctor will monitor follicular development via ultrasound. These ultrasounds will be done to count the number of developing follicles. They will also be measured.

Millimeters are used to measure follicle size (mm). Typically, when your follicles are just about to reach their full mature size, your doctor will want to schedule your trigger shot—or hCG/LH injection. This measures about 18 mm. The size of a mature follicle that is going to ovulation ranges from 18 to 25 mm.

How many follicles are required for the treatment of infertility?

For various fertility therapies, a particular number of follicles is ideal. For in vitro fertilization (IVF), for instance, you require more follicles.

Follicles required for Clomid Cycle

Ideally, a Clomid cycle should only result in one or two healthy follicles. When you learn that just one or two follicles are big enough to ovulate, you can feel disheartened. Though, more isn’t always better. Every mature-sized follicle had the capacity to produce an egg, which had the potential to be fertilized.

Twins are possible if you have two follicles. Or you can have a single birth. Or perhaps you won’t get pregnant at all. Pregnancy isn’t always guaranteed by ovulation.

Follicles required for Gonadotropins Cycle

Similar to Clomid, you should aim for one or two mature follicles. Multiple pregnancies are more likely when gonadotropins, injectable fertility medications, are used. Three, four, or even more mature follicles may form.

Your doctor might stop your treatment cycle if you develop four or more follicles. This could entail postponing an IUI process, skipping the trigger shot, or restricting you from having sex for a certain period of time.

It’s critical that you heed your doctor’s advice if they advise against having sex. With so many developed follicles, the likelihood of producing triplets or quadruplets is considerable. The risk of multiple pregnancies poses a danger to both you and your unborn children. It is better to wait and try again on a different cycle is preferable.

Follicles required for one IVF Cycle

Your doctor hopes to stimulate multiple mature follicles in your ovaries throughout IVF treatment. An acceptable number of follicles is regarded as falling between 8 and 15.

Your doctor will use an ultrasound-guided needle to aspirate the follicles during an egg retrieval. Not every follicle will contain an egg of sufficient quality. So don’t be shocked if there are fewer eggs recovered than the estimated number of healthy-sized follicles you have.


  • Can I become pregnant if my ovarian reserve is low?

Yes, even with a decreased ovarian reserve, you can still become pregnant. When your ovarian reserve is poor, your chances of getting pregnant may be lower, but you only need one egg to become pregnant. The egg count is not the only determinant in conceiving. Getting pregnant also heavily depends on your uterus’ and fallopian tubes’ general health, the quality of your eggs and sperm, and other factors.

  • Does taking folic acid help to enhance the quality of eggs?

Folic acid is found in prenatal vitamins, which are crucial for preserving egg quality. If you want to get pregnant, your healthcare professional will advise you to start taking prenatal vitamins. Prenatal vitamins should ideally be taken at least three months before conception. Your eggs’ health is influenced by your diet, your exercise routine, and other lifestyle choices (or quality). However, it has no impact on your egg count or the number of eggs.

  • How effective is IVF when the ovarian reserve is low?

The cause of poor ovarian reserve, the number of eggs you have, and how your body reacts to fertility medicine all affect IVF success rates. Unknown success rates for IVF in those with a depleted ovarian reserve. IVF success rates decrease with age, much like with natural pregnancies, according to researchers. Those who have a decreased ovarian reserve are included in this. You are less likely to respond well to ovarian stimulation medication if screening tests reveal that you have a poor ovarian reserve, but it may still be the best option for you. You should talk to a fertility expert about this.


Stress can be caused by the size and number of follicles. It can be very challenging to deal with a poor ovarian reserve diagnosis, or it might leave you wondering what happens next. Don’t give up on your desire to have a parent because you have a decreased ovarian reserve; there are treatments available to assist you. Just remember that it is possible to conceive while suffering from this disease, so don’t give up hope. With your remaining egg supply, your healthcare professional can develop a treatment strategy that aids in your pregnancy goals. Your doctor might advise IVF using donor eggs, a route that not all couples are able to or want to follow.

Although follicle counts are a significant predictor of fertility, keep in mind that a single figure does not define you or even accurately forecast your future fertility. Consult your doctor if you’re unsure about what your follicle counts signify. Never be reluctant to get a second opinion on the findings of a fertility test or diagnostic. And don’t forget to ask for help. Testing and treatment for infertility are stressful. You don’t have to accomplish this by yourself.

Srujana Mohanty
She is the Managing Editor of Cogito137, one of India’s leading student-run science communication magazines. She's been working in scientific and medical writing and editing since 2018, also associated with the quality assurance team of scientific journal editing. Majored in Chemistry with a minor in Biology at IISER Kolkata, Srujana loves doodling and watching series.


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