How do Follicles Contribute to IVF Success?

A woman’s ovaries already contain all the eggs she is ever going to have in her lifetime at birth. As the years go on, a large number of these eggs will be lost via natural cell death (apoptosis) and through a process known as atresia, where approximately 15-20 immature follicles present in the ovaries “vie” to mature and free an egg in the time of ovulation. Each unsuccessful follicle is reabsorbed into the body. The speed of this process increases with age until the ovaries stop egg release and menopause sets in.

A lot of women who need help to get pregnant are worried about the number of eggs remaining in their ovaries, or their ovarian reserve. Reduced ovarian reserve, whether it is caused by the approach of premature menopause or by natural aging, is a leading cause of women’s infertility. It can as well be a huge factor when it comes to how likely in vitro fertilization (IVF) will yield a positive outcome for a patient. Knowing how your ovaries work as well as how the follicles in your ovaries affect the chances of a successful IVF cycle is an important part of selecting a fertility treatment plan with your fertility doctor.

What are ovarian follicles, and why are they essential for IVF?

Follicles refer to small, fluid-filled sacs found in the ovaries, in which female eggs become mature. Ovulation is said to take place when the follicle sack in the ovaries bursts and the egg is set free. Normally, only a single egg attains full maturation and is subsequently released. However, during an IVF cycle, ovarian stimulation medications, like FSH (follicle stimulating hormone), are used to induce the ovaries to mature higher numbers of eggs all at a time. A higher number of eggs means higher odds for fertilization in the IVF laboratory and pregnancy after the embryo is transferred.

Follicles pass through different stages in the course of their lifetimes. Two of them are essential in the in vitro fertilization (IVF) process:

Antral Follicles: These are small immature follicles that are between 2 to 9-millimeters-long, which is large enough to be visible with an endovaginal ultrasound at the onset of a menstrual cycle. Also called “resting” follicles, antral follicles are an indicator of the ovarian reserve of a woman. From the number of these follicles, fertility experts can make an estimate of the small primordial follicles still left in a woman’s ovaries as well as how well a female will respond to ovarian stimulation medications used in IVF.

Mature Follicles: During ovarian stimulation, you are going to visit the IVF clinic so fertility experts can keep tabs on the size and number of growing follicles. Ideally, a viable and mature follicle that is ready for egg release needs to be around 20 millimeters long.

How many antral follicles need to be there for a good response to IVF?

Sadly, there’s no exact number: the body of every woman is unique, and the same goes for her reaction to ovarian stimulation. There are also other factors that can determine whether an IVF cycle will be successful or not. Moreover, counting antra follicles isn’t an exact science. Based on how experienced the ultrasonographer is, the total count may differ. A technician may see 10, while another counts 11 or 12. However, antral follicle counts can generally be used to determine the right dose of fertility medications to take. Fertility experts consider 15 to 30 a good number.

How many mature follicles need to be there before triggering ovulation for IVF?

While we all know antral follicle, counts are a great indication of IVF success, it is the total number of mature follicles after ovarian stimulation that seems to determine the number of eggs available for fertilization. The IVF cycle might be terminated before egg retrieval if the follicles did not mature.

Normally, fertility clinics would love to see at least four mature follicles prior to the trigger shot.

Once more, there is no exact number. Both follicle quality and quantity are important here. Some patients proceed with very few ovarian follicles, as long as the egg quality is high enough to guarantee successful fertilization and embryo transfer. Too many follicles may also be an issue. A patient with 30 or more mature follicles may also need to stop a trigger shot and the cycle if the fertility expert discovers that she stands a risk of developing OHSS (ovarian hyperstimulation syndrome).

All in all, although follicle counts are useful indicators in IVF, the success of an IVF cycle does not end with them. A woman who has a high number of antral follicle counts may not have viable eggs in the end due to issues with a secondary complicating condition or overstimulation. Conversely, a woman with fewer antral follicle counts may end up having a successful IVF cycle because, while it is better to have more eggs, only one egg can be enough in some cases. Choosing whether to proceed with an IVF cycle or not based on the mature or antral follicle counts is a decision that you and your fertility doctor need to make.

If you have any questions regarding the IVF process, we’re here to help! You can reach out to us at or www.coastalfertility.com or call (949) 726-0600.