Antral Follicle Counts

Ovarian Reserve and Egg Supply

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 future. In short, a woman's ovarian reserve is her remaining fertility potential.

While there are some ovarian reserve screening tests, they are far from perfect.

There are several ways that we try to predict "egg quantity and quality" as well as trying to estimate chances for conception with various fertility treatments. Some important variables involved are:

• Female age
• Day 3 FSH levels
• AMH blood levels

The response of the ovaries to ovarian stimulation with injectable gonadotropins is another important variable affecting chances for conception when we attempt in vitro fertilization.

What is 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 (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. So when there are only a few antral follicles visible, there are much less eggs remaining as compared to when there are more antral follicles. As women age, they have less eggs (primordial follicles) remaining, therefore they have fewer antral follicles 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 give injectable FSH medications that are used for in vitro fertilization. The number of eggs retrieved correlates with IVF success rates.

• 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.
• 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.
• 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.

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 high antral count and volume (ovary = 37 by 19.5mm) This woman had irregular periods and was a "high responder" to injectable FSH medication.

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

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 ovaries for IVF were not successful

How many antral follicles are good?

There is not a perfect answer to this question. 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. 3-5 antral follicles would be indicative of good ovarian

Risk for cycle cancellation according to the antral count

The chance of cancellation when attempting in vitro fertilization is higher with low antral follicle counts. Attempts to do IVF are sometimes "cancelled" when the ovaries respond very poorly to the stimulation meds because success rates are very low with less than 3 mature follicles.

Response to stimulation with gonadotropins (FSH products)

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.

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 injectables will 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.