What Are Antral Follicles? How Many Should You Have?

What Is an Antral Follicle Count? What Do the Results Say About Your Fertility?

ultrasound technician looking at ultrasound screen, used for antral follicle count
A transvaginal ultrasound is used to conduct an antral follicle count. VStock LLC/Tanya Constantine / Getty Images

Quick definition: antral follicles are small follicles (2 to 10 mm in diameter) that are visible on the ovaries via ultrasound. They are also known as resting follicles.

They appear in the beginning of the menstrual cycle. Their number can indicate the amount of microscopic primordial follicles contained within the ovary.

An ultrasound exam to count the number of antral follicles may be performed as a part of fertility testing.

This is known as an antral follicle count (AFC). More on this below.

A low number of antral follicles may indicate poor ovarian reserves. In other words, the total number of eggs left in the ovaries may be low. Low antral follicle counts may also predict a poorer response to fertility drugs meant to stimulate ovulation.

An abnormally high number of antral follicles may indicate PCOS.

What Are Antral Follicles? Why Are They an Important Fertility Predictor?

To understand what antral follicles are, it’ll help to have a basic understanding of follicles.

In the ovary, follicles are tiny fluid-filled sacs that contain immature eggs, or oocyte. Every follicle contains one egg. You are born with all the eggs you will ever have. As time passes, follicles (and eggs) die. This begins even before birth.

An unborn baby girl has the most eggs she will ever have when she is just 12 weeks gestation. At this time, the ovaries contain 6 to 7 million follicles.

By the time that girl’s first period comes, she will have just 500,000 left.

Less than 1% of the follicles in your ovaries will ever reach ovulation.

Theoretically, if we could know how many follicles are inside your ovaries, we could have an idea of how many eggs you have left.

Unfortunately, it is impossible to count the total number of potential eggs (or follicles) inside the ovaries.

Follicles start off very, very small.

All the follicles in the ovary start off as primordial follicles. A primordial follicle is just 25 micrometers. That is 0.025 millimeters. It is impossible to see with the naked eye, let alone on an ultrasound.

Every day, primordial follicles are “awakened” by hormonal signals. They start to mature. As long as they continue to survive and graduate to the next stage, they grow larger and larger.

One of those stages is the tertiary stage. During this time, the follicle gains a fluid filled cavity known as the antrum. Follicles with an antrum are known as antral follicles.

An antral follicle measures between 2 and 10 mm in diameter.

For some perspective, an antrum follicle that is now 5 mm is 200 times bigger than it was as a primordial follicle!

Antrum follicles are finally visible on the ultrasound. Research has found that the number of active antrum follicles on the ovaries correlates to the potential number of eggs left.

We still can’t know how many follicles total there are. But when a woman has very few antral follicles developing on the ovaries, we know her ovarian reserves are low.

Having low ovarian reserves doesn’t mean you can’t get pregnant. But it does mean your ovaries may not respond to fertility drugs as well as a woman with better ovarian reserves.

What Is an Antral Follicle Count (AFC)?

An antral follicle count is a fertility test. It’s done via transvaginal ultrasound, sometimes between cycle day 2 and 5.

The ultrasound tech will look at each ovary and count the number of follicles measuring between 2 and 10 mm.

Your doctor may order this test in order to...

  • Help diagnosis polycystic ovarian syndrome
  • Give you an idea of where your fertility stands in relation to your age (do you have more, less, or an average number of follicles compared to others your age)

The test may be done as part of a fertility workup. Or, it may be ordered before a fertility treatment cycle.

Having too few antral follicles may indicate your ovaries won’t react well to fertility drugs.

The skill of the ultrasound technician and the ultrasound equipment itself can affect the results. If one center gets a poor result, consider getting a second opinion.

How Many Antral Follicles Are Normal?

Remember that it is normal for your ovarian reserves to go down as you age. So, what’s normal for a 25 year old isn’t necessarily normal for a 38 year old.

An antral follicle count of 3 to 6 is considered low.

Again, remember, this doesn’t mean you can’t get pregnant. It only means your ovaries may not react well to the fertility drugs.

One study conducted antral follicle counts in women with proven fertility. (Most studies on AFC were done on infertile women.)

To be included in this study, the woman had to...

Here were their average antral follicle counts (AFC), along with the range seen (from the lowest to highest AFC count.)

Age rangeAverage AFCLowest AFCHighest AFC
25 to 3415330
35 to 409125
41 to 464117


Jayaprakasan K1, Campbell B, Hopkisson J, Johnson I, Raine-Fenning N. “A prospective, comparative analysis of anti-Müllerian hormone, inhibin-B, and three-dimensional ultrasound determinants of ovarian reserve in the prediction of poor response to controlled ovarian stimulation.” Fertil Steril. 2010 Feb;93(3):855-64. doi: 10.1016/j.fertnstert.2008.10.042. Epub 2008 Nov 30. http://www.fertstert.org/article/S0015-0282%2808%2904262-3/abstract

Kwee J1, Elting ME, Schats R, McDonnell J, Lambalk CB. “Ovarian volume and antral follicle count for the prediction of low and hyper responders with in vitro fertilization.” Reprod Biol Endocrinol. 2007 Mar 15;5:9. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1847823/

Ovarian Reserve Testing. Committee on Gynecologic Practice. Number 618, January 2015. The American College of Obstetricians and Gynecologists. Accessed February 22, 2016. http://www.acog.org/Resources-And-Publications/Committee-Opinions/Committee-on-Gynecologic-Practice/Ovarian-Reserve-Testing

Scheffer GJ1, Broekmans FJ, Looman CW, Blankenstein M, Fauser BC, teJong FH, teVelde ER. “The number of antral follicles in normal women with proven fertility is the best reflection of reproductive age.” Hum Reprod. 2003 Apr;18(4):700-6. http://humrep.oxfordjournals.org/content/18/4/700.full

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