Antral Follicle Counts, Resting Follicles and Ovarian Reserve
Testing egg supply and predicting response to ovarian stimulation

Page author Richard Sherbahn MD

IVF success rate by antral count 2007-2010 data from our program Age under 35 years old	Number of eggs retrieved at IVF by antral count 2007-2010 data from our program Age under 35 years old
Details on antrals and IVF outcomes for other age groups is below

What Are Antral Follicles?

Antral follicles are small follicles (about 2-8 mm in diameter) that we can see - and measure and count - with ultrasound. Antral follicles are also referred to as resting follicles.

Vaginal ultrasound is the best way to accurately assess and count these small structures. In my opinion, the antral follicle counts (along with female age) are by far the best tool that we currently have for estimating ovarian reserve, the expected response to ovarian stimulating drugs, and the chance for successful pregnancy with in vitro fertilization.

Presumably, the number of antral follicles visible on ultrasound is indicative of the relative number of microscopic (and sound asleep) primordial follicles remaining in the ovary. Each primordial follicle contains an immature egg that can potentially develop in the future.

When there are only a few antral follicles visible, there are far fewer eggs remaining as compared to when there are more antrals. As women age, they have less eggs (primordial follicles) remaining and they have fewer antral follicles.

Antral follicle counts are a good predictor of the number of mature follicles that we will be able to stimulate in the woman's ovaries when we give injectable FSH medications that are used for in vitro fertilization. The number of eggs retrieved correlates with IVF success rates.

1. When there are an average (or high) number of antral follicles, we tend to get a "good" response with many mature follicles. We tend to get a good number of eggs at retrieval in these cases. Pregnancy rates are higher than average.
   
   
2. When there are few antral follicles, we tend to get a poor response with few mature follicles. Cancellation of an IVF cycle is much more common when there is a low antral count. Pregnancy rates are lower overall in this group. The reduction in success rates is more pronounced in women over 35 years old.
   
   
3. When the number of antral follicles is intermediate, the response is not as predictable. In most cases the response is intermediate. However, we could also have either a low or a good response when the antral counts are intermediate. Pregnancy rates are pretty good overall in this group.

More on egg quantity and quality issues and ovarian reserve

High ovarian volume and high antral follicle counts
Ultrasound image of an ovary at the beginning of a menstrual cycle. No medications being given. The ovary is outlined in blue. There are numerous antral follicles visible - marked with red. 16 are seen in this image. Ovary had a total of 35 antrals (only 1 plane is shown). This is a polycystic ovary, with a high antral count and high volume (ovary = 37 by 19.5mm) This woman had irregular periods and was a "high responder" to injectable FSH drugs.

Normal ovarian volume and "normal" antral follicle counts
Ultrasound image of an ovary early in the menstrual cycle. No medications being given. The ovary is outlined in blue. 9 antral follicles are seen - marked with red. The ovary has normal volume (cursors measuring ovary = 30 by 18mm). Expect a normal response to injectable FSH.

Low ovarian volume and low antral follicle counts
An ovary is outlined in blue and is small (low volume) with only 1 antral
Her other ovary had only 2 antrals
She had regular periods and a normal day 3 FSH test
Attempts to stimulate her "sleepy" ovaries for IVF were not successful

How many antral follicles is "good"?

There is not a perfect answer to this question. Unfortunately, we do not live in a perfect world, and some ovaries have not yet read up on antral follicle counts to know how they are supposed to respond to stimulation.

Antral follicle counts can also be somewhat "observer-dependent". This means that if we had several different trained ultrasonographers do an antral count on a woman, they would not all get exactly the same result. Therefore, what we decide looks like 6 antral follicles, at another clinic might have been read as 4 or 8, etc.

From our own observations and experience, here are some general guidelines:

Correlation of antral counts and IVF outcomes

As shown below, there is a strong association between antral numbers and:

• Ovarian response to stimulating medications
• Chances for IVF success
• Risk of having a cancelled cycle

In the charts below:

• Live birth success rates shown by green columns
• Rate of cycle cancellation before egg retrieval shown by yellow columns
• Average number of eggs retrieved shown by red text

Antrals and IVF Success - Female age under 35
IVF live birth rates are reduced with low antral follicle counts
Women with low antral counts give fewer eggs and have higher cycle cancellation rates
The average antral follicle count in women under age 35 age was 28

Antrals and IVF Success - Women of ages 35-37
Women 35 to 37 years old have somewhat lower success than the under 35 group
Higher rates of cycle cancellation are also seen
The average antral follicle count at age 35-37 was 21

Antrals and IVF Success - Female age 38-40 years
The average antral follicle count at age 38 to 40 was 15

Antrals and IVF Success - Female age 41-42
Women age 41 to 42 have substantially lower success rates
Having more than 22 antrals was best
The average count at this age was only 13

The above data is from our IVF program at the Advanced Fertility Center of Chicago

As seen in the above charts, the chance of "cancellation" when attempting in vitro fertilization is higher with low antral follicle counts. IVF attempts are sometimes "cancelled" when the ovaries respond very poorly to stimulation meds. This is because success rates are very low when less than 3 mature follicles are present on ultrasound.

More about IVF cycle cancellation

Response to stimulation with gonadotropins (FSH drugs)

The level of response of the ovaries when the woman takes injectable FSH for stimulation is often predictive of the egg quantity and quality - and therefore, also the relative chances for success with infertility treatment. The level of response that we will get from ovarian stimulating drugs can be estimated in advance with antral follicle counts (see above table).

There are no absolute and accepted cutoffs for defining "low", "normal", or "high-responders". However, here are some guidelines.

Low responder:

• When stimulated aggressively with injectable FSH will develop less than 5 mature follicles - often requiring high doses of the medications
• Some women will only develop 1 or 2 mature follicles - even on high drug doses
• These women might not be good candidates for IVF using their own eggs and could possibly need IVF with donor eggs
  

• When stimulated aggressively with injectable FSH will develop 5-8 mature follicles as well as several smaller ones
  

High responder:

• When stimulated with injectables can develop about 8 or more mature follicles as well as many small and medium-sized follicles
• These women usually respond briskly to lower doses of medications
• They are at higher risk for ovarian hyperstimulation syndrome

In vitro fertilization is a treatment for infertility and is not done as a "test", but it does give us some information about egg and embryo quality.

• Careful examination of the eggs and embryos during the in vitro incubation process in the laboratory can give us clues about "egg quality"
• For example, eggs may demonstrate poor morphology, may have problems with maturation, or with fertilization, proper cleavage, or blastocyst formation, etc.

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