Unlike men, who produce sperm on an ongoing basis, females are born with a lifetime supply of eggs in their ovaries. By the time a girl reaches puberty, many of those eggs will have been lost through a natural process called ovarian follicle atresia, leaving a woman with around 300,000 eggs. When a girl reaches puberty, each month around 20 ovarian follicles will develop with only one being released.  The rest of the follicles will undergo atresia such that women are not losing only one egg per cycle to ovulation, but rather a large number of eggs.  It is estimated that women will lose close to 1,000 follicles for every follicle that is ovulated.

What is an Antral Follicle?

An antral follicle, also known as a “resting” follicle, is a small, fluid-filled sac that contains an immature egg.  Each month, women create multiple antral follicles which can be viewed, measured and counted by ultrasound examination during their cycle. The best time of the cycle to assess an “antral follicle count” is around day 3 of the menstrual period, before any large follicles have formed on either ovary. The number of antral follicles will vary from month to month and will decline as a woman ages and advances towards menopause. Read more information about Antral Follicle.

Why is Antral Follicle Count so Important?

When determining the fertility potential of a woman, fertility doctors will find out the number of antral follicles she has each month, or her antral follicle count.  They use that information along with her age, and her day 3 hormone level testing of AMH, FSH, estradiol and progesterone to determine her fertility potential.

These tests are used as indicators for estimating how many eggs she has remaining, also known as her “ovarian reserve”, and the woman’s chances for conceiving using her own eggs.  The antral follicles give fertility doctors a good indication of the number of mature follicles that a woman has in her ovaries that can be stimulated by fertility medications during a treatment cycle of in vitro fertilization (IVF).

Antral Follicles and IVF

During a cycle of IVF, a woman’s fertility doctor will prescribe hormone medications that will stimulate as many of her antral follicles to grow as possible that month.

Throughout the IVF cycle, the doctor will use hormone level blood tests and ultrasounds to monitor the development of these antral follicles to select the best timing of when the follicles have developed mature eggs.

When the timing is right, they will prescribe an injectable medication that is used to trigger a release of the eggs and then 24 hours later they will retrieve all of the mature eggs from the ovaries in a procedure called an egg retrieval.  The number of eggs retrieved directly correlates with the success rate of IVF.  The more mature eggs that are retrieved, the higher the changes of having a child through IVF.

What is a Normal Antral Follicle Count?

When an average to high number of antral follicles (8+) are seen by ultrasound, this conveys a better prognosis for fertility treatments such as IVF. Lower numbers of antral follicles, such as 6-8 can be a sign that more aggressive treatments may be needed to optimize the eggs left in a woman’s reserve.

Antral follicle counts from 3-6 do not mean that a woman cannot become pregnant, but treatment should not be delayed if possible.

Antral follicle counts are one of the best tests available that fertility doctors use to measure a woman’s ovarian reserve and fertility potential.