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Houston Fertility Center

How Is Follicle Size and Number Important for IVF Treatment?

By Sonja Kristiansen, MD on December 28, 2018

An eggFor couples who have had difficulty conceiving, in vitro fertilization, or IVF, offers a solution.

When considering IVF, it's helpful to understand how IVF works. While there are many components to IVF and reproduction, here, Dr. Sonja B. Kristiansen takes a closer look at follicle size and number and the role they play in IVF.

If you live in or around Houston, TX and would like more information, we welcome you to contact Houston Fertility Center to schedule an appointment.

Follicles Play an Important Role in Reproduction

Follicles are an important part of a woman's reproductive system. Follicles are small sacs of fluid within the ovaries, where a woman's eggs develop.

A single egg will mature within a single follicle. Once matured, the follicle will open, releasing the egg. Generally, only one egg is released from a follicle during a single menstrual cycle.

Once released, a mature egg will travel down the fallopian tube toward the uterus. At this time, the egg is ready to be fertilized by sperm. If sperm reaches the egg and fertilization occurs, the embryo can travel to the uterus and implant, resulting in pregnancy.

Is the Number of Follicles Important?

For women without fertility issues, the number of follicles an ovary has isn't generally a concern since only one matured follicle is needed to release a single egg during the menstrual cycle.

It should also be noted that, while only one follicle may be visible, the ovaries have many follicles that are microscopic in size and will not be visible until they begin developing an egg.

For those considering IVF, more follicles often leads to a greater number of eggs available for harvesting.

How Many Follicles Are Needed for IVF?

When it comes to IVF treatment, one of the goals is to harvest multiple eggs during a single treatment. In order to accomplish this, multiple follicles must be triggered to produce mature eggs at the same time. This is done through medications that stimulate the ovaries and follicles to produce multiple eggs at once.

Once the follicles become stimulated and grow in size, an ultrasound can be done to count the number of visible follicles. The more follicles that are visible, the larger the egg reserve.

Although there isn't a magic number to how many follicles a woman should have for IVF treatment, a larger amount will generally yield more eggs and more chances of conception.

The Size of Follicles Helps Determine When Eggs Can Be Harvested

Follicles may range in size from microscopic to over 10 mm. Microscopic follicles, called primordial follicles, are follicles that haven't developed or released an egg yet.

Once a follicle is ready to develop an egg, it will fill with fluid and grow in size. This is called an antral follicle.

Antral follicles are often large enough to be seen through an ultrasound test and can be counted during the IVF treatment process. Once a certain size is reached, usually above 18 mm, the follicles will be about ready to release the eggs.

A shot will be administered to trigger the release of the eggs so they can be harvested and fertilized. 

Learn More about Fertility Treatments

For more information about fertility treatments, or to discuss which treatments may be right for you, please call (713) 862-6181 to schedule a consultation.

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