Antral Follicle Counts, Ovarian Reserve & IVF Stimulation Response

Antral Follicle Counts, Resting Follicles, Ovarian Volume and Ovarian Reserve

Women are born with all of the eggs that they will ever have, and they lose them constantly throughout life until menopause, when none remain. It would be helpful to have a reliable test that would tell us how many eggs a woman has remaining at a point in time - as well as telling us about the quality of those eggs. The term "ovarian reserve" is useful in the field of reproductive medicine. It is an estimate of the reserve of the woman's ovaries - remaining egg supply - to be able to make babies in the (near) future. In other words, a woman's ovarian reserve is her remaining fertility potential.

While there are some ovarian reserve screening tests, they are far from perfect. This page will focus mainly on on antral follicle counts, but will also address ovarian volume and ovarian response to injectable FSH stimulation. The ovarian reserve page has more overview information on egg quantity and quality issues, as well as other fertility screening tests.

There are several ways that we try to predict "egg quantity and quality" as well as trying to estimate chances for conception with various forms of fertility treatment. Female age and "day 3 FSH" levels are 2 very important variables. The response of the ovaries to ovarian stimulation with injectable gonadotropins (FSH) is another very important variable that affects the overall chance for conception when we attempt in vitro fertilization.

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 (in conjunction with female age) are by far the best tool that we currently have for estimating ovarian reserve and/or chances for 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. In other words, when there are only a few antral follicles visible, there are less eggs remaining as compared to when there are more antral follicles visible. As women age, they have less eggs (primordial follicles) remaining, therefore they have less antral follicles visible on ultrasound.

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 administer the 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 the 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 very good response when the antral counts are intermediate. Pregnancy rates are pretty good overall in this group.

At least in some women, the antral follicle count may be a good predictor of the number of eggs remaining in the ovaries, as well as the quality of those eggs. I (Dr. Sherbahn) do not believe that this holds true for all women.

For example, we see some women in their early 20's that want to be egg donors at our center that when we do ultrasound on them we see only 3 antral follicles per ovary - and the volume of the ovary is low. Although we no longer accept these women into our egg donor program, I am not convinced that they have an egg quality or quantity problem (my best guess is that they have reduced quantity, but quality is probably fine). Often the young woman is concerned about her future fertility when we tell them that their ovaries are small and do not look like they will make sufficient eggs to be a good donor candidate. However, I am not aware of any data (medical research, etc.) that shows that women in that particular scenario are going to have a fertility problem. They might - but we just don't know. Some of those women already have 3 kids and are more fertile than they would prefer - so we really can't say that all women with low antral follicle counts have a fertility problem (reduced egg quality or quantity).

However, fertile women applying to be egg donors with few antral follicles are probably very different from women that have had difficulty conceiving. Many infertile women with low antral follicle counts do have a problem with both egg quality and quantity. The younger they are, the more likely that the problem is just quantity of eggs, whereas for women in their late 30's and early 40's with reduced antrals, there is often a problem with both quantity and quality.

Antral follicles polycystic & good ovary volume

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

Normal antrals predict good IVF response

Ultrasound image of an ovary at the beginning of a menstrual cycle. No medications are being given.
The ovary is outlined in blue. 9 antral follicles are seen - marked with red spots
The ovary has normal volume (cursors measuring ovary = 30 by 17.8mm)
This woman had regular periods and a normal response to injectable FSH drugs


The left ovary is outlined in blue and is small (low volume) Only 1 antral follicle is seen This woman had regular periods and a normal day 3 FSH test	The right ovary from the same woman This ovary is also small with only 2 antral follicles She only had 3 antrals total - from both ovaries Attempts to stimulate her ovaries for IVF were not successful

There is not a perfect answer to this excellent 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.

Total number of antral follicles	Expected response to injectable ovarian stimulating drug (FSH product) and chances for success
Less than 4	Extremely low count, very poor (or no) response to stimulation and a cancelled cycle expected. Should seriously consider not attempting IVF at all. Rare pregnancies if IVF attempted.
4-7	Low count, we are concerned about a possible/probable poor response to the stimulation drugs. Likely to need high doses of FSH product to stimulate ovaries adequately. Higher than average rate of IVF cycle cancellation. Lower than average pregnancy rates for those cases that make it to egg retrieval. The reduction in success rates is more pronounced beyond age 35.
8-10	Somewhat reduced count. Higher than average rate of IVF cycle cancellation. Slightly reduced chances for pregnancy as a group.
11-14	Normal (but intermediate) count, the response to drug stimulation is sometimes low, but usually good. Slight increased risk for IVF cycle cancellation. Pregnancy rates as a group only slightly reduced compared to the "best" group.
15-26	Normal (good) antral count, should have an excellent response to ovarian stimulation. Likely to respond well to low doses of FSH product. Very low risk for IVF cycle cancellation. Some risk for ovarian overstimulation. Best pregnancy rates overall as a group.
Over 26	High count, watch for polycystic ovary type of ovarian response. Likely to have a high response to low doses of FSH product. Higher than average risk for overstimulation. Very good pregnancy rate overall as a group, but some cases in the group have egg quality issues and lower chances for pregnancy.

This graph shows that cancellation rates of attempted in vitro fertilization cycles are much higher with low antral follicle counts
Cancellation occurs when the ovaries respond very poorly to the medications we give to attempt development of multiple mature eggs.
Because IVF success rates are very low with less than 3 mature follicles develop, egg retrieval and the rest of the IVF cycle are often "cancelled".

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 general 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 very high doses of the medications. These women are not good candidates for IVF using their own eggs - but are good candidates for in vitro fertilization with donor eggs.

"Normal" or "average" responder: When stimulated aggressively with injectable FSH will develop 5-8 mature follicles as well as several smaller ones.

High responder: When stimulated aggressively with injectable FSH will develop about 8 or more mature follicles as well as many more small and medium-sized follicles. These women usually respond briskly to lower doses of the medications. They are also at higher risk for ovarian hyperstimulation syndrome.

We can also challenge the ovaries with drugs (hormones) and assess whether they have responded appropriately in order to distinguish women with good ovarian reserve from women with diminished reserve.

For example, the exogenous FSH ovarian reserve test involves giving an FSH injection on day 3 of the cycle and testing both the baseline FSH and baseline and 24 hour post-injection estradiol to see if a normal response has resulted.

If the estradiol response is poor, ovarian reserve and egg quantity are also likely to be poor. The woman is also less likely to be a "normal responder" to gonadotropin stimulation.

This is a treatment for infertility and is never done as a "test", but at the same time it gives much useful information about egg and embryo quality. By careful examination of the eggs and embryos during the in vitro incubation process we sometimes see things that gives us clues about the wife's "egg quality".

For example, the eggs may demonstrate poor morphology, or may have problems with maturation, or with fertilization, proper cleavage, etc.

Treatment options for women with low antral follicle counts and low response to stimulation: