An Antral Follicle Count (AFC) is a diagnostic measurement used in reproductive medicine to estimate a woman’s ovarian reserve, which is the remaining supply of eggs within the ovaries. This non-invasive test offers a snapshot of the current number of small, resting follicles available to potentially mature during a menstrual cycle. The AFC is determined through a transvaginal ultrasound procedure, providing physicians with quantitative data about a patient’s fertility potential. It serves as one of the most reliable tools for assessing the capacity of the ovaries to produce eggs.
The Biology Behind the Count
The antral follicle represents a specific stage in the continuous process of follicular development within the ovary. Every woman is born with a finite number of microscopic primordial follicles, each containing an immature egg, which serve as the entire reserve for her reproductive lifespan. These primordial follicles are continually activated to progress through several stages, transforming into primary and then secondary follicles, but they remain too small to be seen using standard ultrasound technology.
The antral stage is reached when the follicle develops a fluid-filled cavity known as the antrum, making it visible via ultrasound. The number of visible antral follicles acts as a proxy for the size of the total, invisible pool of remaining primordial follicles. Therefore, the AFC is not a direct count of a woman’s entire egg supply, but rather an indicator of the number of eggs that have been recruited for development in a given cycle. A higher AFC suggests a larger overall ovarian reserve is present, while a lower count indicates a diminished reserve.
How the Antral Follicle Count is Measured
The Antral Follicle Count is obtained through a specialized transvaginal ultrasound, which offers a close and clear visualization of the ovaries. This procedure is performed by inserting a small, lubricated probe into the vagina, allowing the sonographer to capture detailed images of both ovaries. The timing of the scan is standardized to ensure accuracy, typically taking place between day two and day five of the menstrual cycle, during the early follicular phase.
During the scan, the specialist systematically identifies and counts all follicles that fall within a specific size range in both ovaries. An antral follicle is generally defined as having a diameter between 2 and 10 millimeters. Follicles smaller than this are not yet considered antral, and those larger than 10 millimeters are likely already maturing, which would skew the baseline count. The resulting total sum from both ovaries provides the final AFC number.
Interpreting the Results
The numerical result of an Antral Follicle Count is strongly correlated with a woman’s age, since ovarian reserve naturally declines over time. A high AFC, generally considered to be a total count of 22 to 35 follicles, suggests an excellent ovarian reserve and a robust response to hormonal stimulation if needed. Conversely, a total count below 5 to 7 is commonly classified as a low AFC, indicating a diminished ovarian reserve.
An average or expected count for women of reproductive age often falls within the range of 10 to 20 total follicles. This range typically predicts an adequate response to fertility treatments. While a low AFC signals a reduced quantity of eggs, it does not mean that natural conception is impossible, as only a single healthy egg is required for pregnancy. However, it does suggest a potential for lower success rates in procedures that depend on retrieving multiple eggs. The count serves as a measure of quantity, but it does not provide information about the quality of the eggs, which remains primarily linked to a woman’s age.
AFC in Clinical Context
The Antral Follicle Count is a fundamental tool for fertility specialists, as it helps predict how the ovaries will respond to medication used in assisted reproductive treatments like In Vitro Fertilization (IVF). The count is a strong predictor of the number of eggs a physician will be able to retrieve following ovarian stimulation, which is crucial for designing a personalized treatment plan.
For individuals with a low AFC, doctors may anticipate a poor response to standard medication doses, often referred to as a low responder profile. In these cases, the treatment protocol may be adjusted to include higher doses of stimulating hormones to maximize the recruitment of available follicles. Conversely, a very high AFC can be associated with Polycystic Ovary Syndrome (PCOS) and indicates a risk of Ovarian Hyperstimulation Syndrome (OHSS). For patients with a high AFC, the physician will typically prescribe lower doses of ovarian stimulation medication to mitigate the risk of OHSS. The AFC is often used in conjunction with blood tests for Anti-Müllerian Hormone (AMH), which also reflects ovarian reserve, to provide a more complete picture of the patient’s reproductive status.