Ovarian Follicles

What are follicles?

An ovarian follicle is a pouch-like structure (sac), which is filled with fluid and contains an oocyte (an immature egg).  In the female reproduction system, the follicles can be traced in the ovaries. Around the time of ovulation, a mature egg is expelled from a follicle. While many follicles begin developing during each of your reproductive cycle, generally just one is able to ovulate an egg.

The follicles, which fail in releasing a mature egg, crumble down and this may occur at any juncture of the follicular development. And, this is called atresia. Nearly 99% of all the ovarian follicles crumble and never attain enough maturity to ovulate/release an egg.

Ensuing ovulation, the follicle, which releases an egg, becomes a corpus luteum.   The corpus luteum produces the progesterone and estrogen hormones that help in preparing the uterus in anticipation of a probable conception.

The development and growth of follicles are monitored during the course of your infertility treatments. For superovulation, which is kindled in IVF treatment, the sheer objective is to stimulate your ovaries for developing many mature follicles in one go.

How to count your Ovarian Reserve

It is impracticable to calculate how many follicles are there in your ovaries as they are too tiny to be seen. Nonetheless, they can be seen through ultrasound once they attain a particular stage of development.

And, this stage recognizes the follicles as antral follicles. Antral follicles are tiny follicles, of the diameter ranging from 2 mm to 10 mm and can be seen on the ovaries through ultrasound. They are also called “resting follicles”. They are generally counted during infertility treatments of a woman.

This is called Antral Follicle Count (AFC). The AFC may give your treating doctor a fair idea of how many feasible eggs have been left in your ovaries. The less Antral Follicles Count may point to your having poor ovarian reserve.

Another way of saying it is you are left with lesser number of eggs in your ovaries. Less Antral Follicle Count may also foretell poor response to the fertility drugs that stimulate ovulation.

An exceptionally high count of Antral Follicles may point to your having Polycystic Ovary Syndrome (PCOS). This is one method of examining and evaluating your ovarian reserve. Antral follicles generate elevated levels of Anti-Mullerian hormones, abbreviated AMH. This hormone is found to be circulating in your blood. Determining AMH levels through your blood tests is yet another method of evaluating your Ovarian Reserve.

Role of Follicles in your Menstrual Cycle?

Your menstrual cycle or periods are divided into two main phases:

  • Follicular phase
  • Luteal Phase

In the follicular phase, follicles in their third level of developmental process are recruited to begin the progression that will finally lead to your ovulation. While many follicles participate in this competition, just one or two eventually attain the full maturity and expel an egg or oocyte.

If you have been taking any kind of fertility drug, many follicles may attain the ovulatory stage. The follicles play a vital role in:

  • Providing nourishment and protection to the oocyte, as it passes through the process of Oogenesis
  • Discharging crucial reproductive hormones, such as inhibin B and estradiol.  These reproductive hormones signal the hypothalamus and the pituitary gland to increase or decrease the release of FSH, Gn-RH, and LH hormones.
  • Turning over into corpus luteum following your ovulation to release the estrogen and progesterone hormones.

Folliculogenesis: The Follicular Development Stages

The follicular development does not begin and end during the follicular stage of your periods. Don’t get surprised to know that the life cycle of follicles begins when a girl is in her mother’s womb. In fact, the life cycle of follicles begins when her ovaries first develop. At this stage, only primordial follicles are present in the ovaries.

Follicles may stay in the undeveloped state for even up to 50 years before they become active to go through the developmental stages. It takes somewhat 6 months to a year for the primordial follicle to grow and become mature enough to ovulate. At all stages of follicular growth, several follicles will discontinue their developmental journey and die.

This way, not all the primordial follicles go through all the developmental stages. Imagine the life of follicles always living in a race of ovulation! While some follicles abandon this race, some others continue to run in the race in the hope of winning (read ovulating an egg). Even less than 1% follicles are able to ovulate an egg. The stages of folliculogenesis are:

  • Primordial follicle – This is the stage when all the follicles are there in the ovaries of a newly-born girl baby.
  • Primary follicles – Some primordial follicles graduate to become primary follicles.  This happens every day during each of the female reproductive cycles beginning in your youth until you enter menopausal phase.
  • Secondary follicles – In this transitional phase, theca cells get involved that help in hormonal secretion.
  • Tertiary follicles are also called antral follicles — In this transitional phase,  follicles include a cavity that is filled with fluid and  known as the antrum. The follicles in this phase can be seen through trans-vaginal ultrasound.
  • Graafian follicle – At this stage the follicles are big enough and ready for ovulating.  Just one or, sometimes, two of the tertiary follicles attain this stage of ovulation maturity during each cycle.
  • Corpus luteum – Corpus luteum is, in fact, are no longer a follicle but the follicle that has transformed itself after releasing an egg.  Corpus luteum release hormones that help in preparing the womb in anticipation of a probable conception.

How Large the Follicles should be?

In case you have been going through some fertility treatments, your treating doctor may like monitoring the follicular development in your ovaries with the help of ultrasound. During a number of ultrasounds, your doctor may like counting the number of growing follicles, besides measuring their size. Follicles are principally measured in mm(s) i.e. Millimeters.

Generally, your treating doctor may like scheduling an hCG/LH shot when your follicles become about the size of around 18 mm and are just near attaining the full maturity. A full-grown follicle, which is near the ovulating point, may measure somewhere between the size of 18 and 25 mm

The number Follicles you may need during your Clomid Cycle?

Though ovulation is not a guarantee for achieving your pregnancy, yet the natural pregnancy just cannot happen without the ovulation. Clomid, Or Serophene, Or Clomiphene Citrate is a drug generally used for inducing ovulation during infertility treatment.

During your Clomid Cycle, you require only one or two follicles of ample size that are all set for ovulation. Every follicle, which is mature enough, may expel an egg and that egg may get fertilized. In case you have two such follicles, there is a possibility of your conceiving twins. And, you may not at all conceive. Or, you may conceive only one child.

The number of Follicles you may need for Gonadotropins Cycle or an IUI?

As in the Clomid Cycle, just one or two mature follicles are ideal in Gonadotropins Cycle or for performing IUI. These injectible drugs for treating infertility are found to be having an elevated risk of achieving multiple pregnancies. There is always a possibility of developing 3, 4 and even more full-grown follicles. If your treating doctor finds more than two full-grown follicles, he or she may decide to call off the treatment cycle.

This would mean calling off your scheduled IUI procedure and your trigger shot, besides advising you to abstain from copulating with your partner in the given reproductive cycle. Adhere strictly to your doctor’s advice of refraining from having sex.  Otherwise, you may run a risk of conceiving three or four babies in the presence of many full-grown follicles. Carrying multiple pregnancies means running the risk of lives to you and your babies. It’s better to wait and try again on another cycle.

The number of Follicles should you need for an IVF Cycle?

While you have opted for an IVF treatment for attaining pregnancy, your doctor may like stimulating your ovaries to acquire full-grown many follicles. Between 8 and 15 mature follicles are well thought-out to be a good amount. In the egg retrieval process, your doctor may draw the follicles with suction guided by an ultrasound needle.

Each and every follicle may not essentially have a quality egg. Don’t  get caught in a surprise, if the retrieved eggs are less in number as compared to the count of full-grown healthy follicles you were informed you had.

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