Ovarian Follicle And It’s Role in Fertility

May 2, 2024
In vitro fertilization (IVF)

Ovaries are part of a woman’s reproductive system that houses the eggs in tiny fluid-filled sacs called ovarian follicles. The eggs stay in these ovaries from the time of the woman’s birth until they are mature enough to descend the fallopian tube during ovulation.

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What is Follicle in Ovary?

Ovarian follicles are tiny fluid sacs that surround a woman’s immature eggs in her ovaries. These eggs start coming down the fallopian tube one egg at a time, every menstrual cycle, once she starts menstruating.  When she reaches puberty, she is left with approximately 300,000 to 400,000 follicles.

The follicles are responsible for influencing the menstrual cycle. Every menstrual cycle, one egg will grow, and mature and the follicle will rupture during ovulation, to release the mature egg.

So, if a woman were to take an ultrasound of her pelvic area, she can know how many follicles are left. Doctors use this information to determine the woman’s fertility, meaning how many follicles and eggs she has left.

Ovarian Follicle Stages

Let’s take a look at the ovarian follicle development stage-wise to get abetter understanding:

Stage 1 - Primary Follicle

This is the first stage where the ovarian follicle starts maturing, ready for release during ovulation. In this stage, germinal cells start surrounding the ovarian follicle, forming layers, and are called the primary follicles.

Stage 2 - Secondary Follicle

In this stage, the primary follicle will mature further. Granular cells form additional layers around the primary follicle and they are now known as secondary follicles.

Stage 3 - Tertiary Follicle

In this stage, two more additional layers of theca – intern a and externa form around the secondary follicle. It will also have an antrum – a space full of fluid. Now, this tertiary follicle is much bigger

Stage 4 - Graafian Follicle

This is the last stage where the oocyte is mature and ready for release during ovulation. This is also the stage in which the corpus luteum forms – to support and promote the implantation of the embryo once it is fertilized by a sperm.

Ovarian Follicles and Fertility

When a woman crosses the age of 35 or is having difficulty conceiving, doctors will suggest taking a fertility test. The fertility test will measure her ovarian reserve by taking a count of the follicles left.

Throughout the life of a woman, many follicles disintegrate or get reabsorbed by the body while only one follicle releases a mature egg. The follicles diminish this way. As the woman ages, the rate of diminishment increases, thus depleting her ovarian reserve. So, the number of ovarian follicles in a woman’s body is directly related to her fertility.

Importance of Follicles

Follicles in the ovaries are very important for a woman. The follicles protect, nurture and secrete the required hormones to help the eggs mature and release during ovulation. Without these follicles, the eggs are not safe and cannot get ready for fertilization.

Fertility issues in women are mostly related to these follicles. They can be broadly classified into two types:

·      Premature Ovarian Insufficiency – Here the woman’s ovaries stop working much before expectation. When a woman has trouble getting pregnant, suffers from irregular periods, or shows early signs of menopause, the doctors check for this condition first.

·      PCOS – Polycystic Ovarian Syndrome is another condition that results in irregular periods, decreased fertility, and hormonal imbalances. When the follicles do not go through the four stages and develop as they should, it can result in PCOS. This will affect the woman’s fertility and can also lead to an excess number of ovarian cysts formation.

What is the Usual Count of Antral Follicles?

A normal antral follicle count is when each of the ovaries has about 5-10 antral follicles. These follicles must be about 2-100 mm in diameter. Remember, the antral follicle count is indirectly proportional to a woman’s age.

The higher the woman’s age, the lower will be the antral follicle count. So, for women between the ages of 25 and 34, an antral follicle count of 9 to 12 is normal. For little older women – between the ages of 35 and40 years, the antral follicle needs to be between 5 and 9. For women between 41and 46 years of age, the antral follicle count can be 5 or lower.

What is Dominant Follicle in Ovary?

Out of the many follicles, the one that reaches the maturity level is known as the dominant follicle in the ovary. In a natural menstrual cycle, only one or very rarely two dominant follicles can be seen. When it comes to fertility treatments, medications increase the number of mature eggs, as more the mature eggs, the higher the chances of conceiving.

What is Empty Follicle Syndrome?

Empty follicle syndrome is also known as EFS. Follicular Aspiration stimulates the ovaries to retrieve oocytes. When this procedure does not provide any oocytes to retrieve, it is known as empty follicle syndrome.

Doctors will administer HCG to help increase the number of oocytes for retrieval. When the HCG level is optimal but no oocytes are retrievable it is known as genuine EFS. If there are no oocytes for retrieval due to low HCG levels, it is known as false EFS.

Must read : Living with PCOS: Risks, Management, and Treatment


Ovarian follicles are an integral part of a female’s fertility. A lack of or malfunctioning of these ovarian follicles has a direct impact on a woman’s fertility. The higher the ovarian follicle reserve, the higher the chances of pregnancy. Similarly, the lower the ovarian follicle reserve, the lower the chances of pregnancy.


Can you get pregnant with a single mature follicle?

Yes, you can get pregnant until your mature follicle releases into the fallopian tube and goes down the tube to meet a sperm. Every menstrual cycle only one such follicle is released, so you can still get pregnant.

How many immature follicles show Polycystic Ovary Syndrome?

If the scan shows 12 or more follicles in each ovary, and if these follicles measure over 2- 9 mm in diameter.