Basal antral follicle count (AFC) is a common ovarian reserve test that gives insight into a woman’s remaining egg supply by using ultrasound to count resting follicles in the ovaries. It’s essentially an ultrasound-based ovarian egg count test that helps fertility specialists assess how many potential eggs you have at a given time. Along with blood hormone tests, the AFC scan is a key part of initial fertility evaluation tests for those seeking fertility advice or treatment. It provides a snapshot of your ovarian reserve, the quantity of eggs left, which is an essential aspect of your reproductive potential.
During a fertility workup or ovarian function assessment, the antral follicle count is often done alongside hormone measurements (like FSH and AMH). This combined approach offers a comprehensive view of ovarian health. By measuring hormone levels and performing an AFC ultrasound, doctors get a clearer picture of both the hormonal environment and the actual number of follicles in the ovaries.
What Is Basal Antral Follicle Count (AFC)?
Basal antral follicle count refers to counting the small “antral” follicles visible in your ovaries via ultrasound at the beginning of a menstrual cycle. Antral follicles are tiny fluid-filled sacs (about 2–10 mm in diameter) within the ovaries, each containing an immature egg. The antral follicle count test measures how many of these small follicles are present in both ovaries, which in turn helps estimate the number of eggs you have remaining. The AFC is an indicator of the quantity of eggs left in your ovaries. Importantly, while the AFC reflects egg quantity, it does not assess egg quality. It tells how many, not how healthy. Every woman is born with all the eggs she will ever have, and this supply declines over time. By adulthood and with each cycle, a subset of dormant eggs begins to grow inside follicles. Antral follicles are those visible early in the cycle that have grown to a small size and can be counted on ultrasound.
Think of antral follicles as the “potential contenders” for ovulation in a given month. At the start of each cycle, a group of these small follicles begins to develop. Only one follicle will become the dominant one that ovulates an egg; the rest will stop growing and eventually disappear. The number of antral follicles seen reflects how many recruits your ovaries bring into that cycle, which correlates with the overall reserve of eggs. A higher AFC suggests a larger pool of remaining eggs, while a low AFC suggests a diminished pool. Doctors consider the AFC as one measure of ovarian reserve, alongside hormone tests. Together, these indicators provide a more comprehensive picture of a woman’s fertility potential at that moment.
How Is the AFC Test Performed?
The antral follicle count is determined through a pelvic ultrasound, usually a transvaginal ultrasound exam done in the very early days of your menstrual cycle. “Basal” refers to the baseline state, typically day 2, 3, or 4 of the cycle. At this time, your ovaries are in a resting state before any one follicle becomes dominant, allowing the doctor to see and count all the small antral follicles present clearly. During the procedure, you will lie back as a thin ultrasound probe is inserted into the vagina to visualize the ovaries up close. The scan itself only takes a few minutes and is generally well tolerated, with at most mild discomfort for some patients. The doctor or sonographer will methodically count the number of small follicles visible in each ovary on the screen.
Timing is important. The scan is scheduled early in the cycle before larger follicles develop. By doing the ultrasound at this basal time, the physician ensures that no follicle has grown big enough to overshadow the others, which could cause smaller ones to be missed. It’s a straightforward test: no special preparation is usually needed aside from timing it with your cycle. The procedure is relatively quick and non-invasive, aside from the internal ultrasound probe.
A fertility specialist or trained ultrasound technician performs the AFC scan at a clinic. If you visit a clinic for ovarian reserve testing or an IVF clinic for an evaluation, the AFC ultrasound will likely be one of the first steps. The scan is often done in the doctor’s office or the fertility center’s ultrasound suite. During the scan, you might even be able to see the tiny black circles (follicles) on the screen as they are counted. Many patients find it fascinating to visualize their ovaries and see the follicles – it makes the concept of “egg count” much more tangible. The clinician will record the number of antral follicles in each ovary. You might hear something like “we see 8 follicles on the right ovary and 6 on the left,” meaning a total AFC of 14. This number will then be interpreted in the context of your age and fertility goals.
It’s worth noting that the AFC ultrasound at the cycle’s start is different from a follicle tracking ultrasound used later in the cycle or during treatments. Follicle tracking ultrasounds are performed mid-cycle to monitor the growth of follicles and determine when one is ready to release an egg or be retrieved. Those scans track the leading follicles as they grow larger. In contrast, the basal AFC scan specifically examines the small resting follicles at the beginning of the cycle, before any have begun rapid growth. Both involve ultrasound imaging of the ovaries, but their timing and purpose differ. The basal AFC tells you how many small follicles are present, whereas tracking ultrasounds later tells you how those follicles are growing in that cycle.
Why Antral Follicle Count Matters for Ovarian Reserve
The antral follicle count is a crucial indicator of ovarian reserve. It helps measure the remaining egg supply in your ovaries. Along with age, antral follicle count is one of the strongest predictors of how the ovaries will respond to fertility treatments and the number of eggs that might be retrieved in an IVF cycle. A higher AFC generally signals a greater quantity of remaining eggs and often correlates with a better response to ovarian stimulation, whereas a low AFC can be a red flag for diminished ovarian reserve.
Why does this count matter so much? The number of antral follicles visible on ultrasound is thought to reflect the number of microscopic primordial follicles still left in the ovaries. Each antral follicle was one of those dormant follicles that has recently grown to the small “antral” stage; for every antral follicle we see, there are many more microscopic ones behind it, but those reserves are not unlimited. As women age and use up their egg supply, fewer follicles reach the antral stage each cycle, so the AFC drops. Ovarian reserve markers like AFC essentially give a window into how far along you are in that egg supply. For example, a woman in her late 20s might have an AFC in her teens or 20s, indicating a robust reserve, while another woman in her 40s could have an AFC of only a few, indicating much lower reserves. The AFC is not a direct measure of fertility, but it is very informative for understanding reproductive potential and planning purposes.
Comparing AFC with Other Ovarian Reserve Markers
AMH and ovarian reserve are closely connected because AMH is a hormone produced by the same small antral follicles that are counted on ultrasound. Each antral follicle secretes a bit of AMH, so the AMH level in your blood correlates with how many small follicles you have. A high AMH generally means a high AFC, and a low AMH corresponds to a low AFC. Both AFC and AMH tend to decline as a woman ages and her egg supply diminishes. In modern fertility practice, AMH and AFC are considered the go-to measures of ovarian reserve, often preferred over older tests like FSH. These newer markers are more predictive of ovarian response to treatment than FSH levels. FSH (measured on day 3 of the cycle) tends to rise only when the ovaries are already quite low on eggs, so it’s a later indicator. By contrast, AMH and AFC can detect subtler declines earlier and with more consistency.
Follicle Count by Age: What’s Normal?
It’s well established that a woman’s ovarian reserve declines with age, and the follicle count by age reflects this steady downward trend. One large study of women ages 25 to 46 found that the AFC declines by roughly 5% per year in the early to mid-30s, and then the decline accelerates to about 12% per year after the late 30s. This helps explain why fertility drops more sharply for women in their 40s compared to their early 30s. To put the numbers in perspective, consider these typical ranges observed in clinical practice:
- In your 20s: An AFC often in the range of 15–30 follicles (high ovarian reserve).
- In your 30s: An AFC averaging around 10–20 follicles in the early 30s, down to maybe 8–15 by the late 30s (moderate reserve, with a gradual decline over the decade).
- By your early 40s: An AFC that is frequently in the low single digits (perhaps 3–10 follicles or fewer), indicating low ovarian reserve.
- Mid-40s and beyond: An AFC that may drop to only a few follicles or even zero in the years approaching menopause.
It’s also important to emphasize that these age-related numbers are about quantity, not quality. Age impacts egg quality independently. Even if a 42-year-old somehow had an AFC of 15 (which is high for that age), the proportion of genetically regular, healthy eggs among those would still be lower than in a 32-year-old with the same count. Age is the most significant factor in egg quality. So while a higher AFC in one’s 40s is certainly better than a low AFC in the 40s, it doesn’t entirely negate the age factor. What the follicle count by age really provides is a sense of where you stand relative to the expected ovarian reserve for your age group, which can inform urgency and options.
Limitations and Considerations of the AFC Test
While the basal antral follicle count is an instrumental test, it’s not a crystal ball. There are important limitations and things to keep in mind when interpreting the results. First and foremost, AFC measures quantity, not quality. Egg quality is primarily determined by age, and unfortunately, there is no direct test for quality aside from seeing how eggs and embryos perform in IVF.
Another consideration is the natural variation and subjectivity in the AFC. The number of antral follicles can actually fluctuate a bit from cycle to cycle. It’s usually in a similar ballpark, but you might have 12 one month and nine the next, for example. This is normal biological variation. One low reading isn’t a definitive verdict. Doctors sometimes repeat the ultrasound in another cycle if the results seem inconsistent or borderline. Additionally, the AFC count is somewhat operator-dependent. Different ultrasound technicians or physicians might count slightly differently, especially if some follicles are right at the margin of visibility or size. Certain conditions and external factors can also affect the antral follicle count. If you are on hormonal birth control, for example, your AFC might appear reduced because the pill suppresses follicle development. In women on the pill or other ovarian-suppressing drugs, the AFC is still countable but could be lower than their natural baseline. Pregnancy and breastfeeding can also temporarily alter ovarian activity.
A basal antral follicle count is a simple yet powerful tool in the world of fertility. With a quick ultrasound, doctors can estimate the quantity of eggs remaining and gain insight into your reproductive potential. This ultrasound-based count of ovarian follicles provides information that can guide decisions on fertility treatments, timing, and expectations. It’s an integral part of an ovarian health check for women planning for the future or struggling to conceive. However, it’s also just one part of the puzzle: the AFC tells us how many eggs might be available, but not how good those eggs are. Results should always be interpreted in context, alongside age and other tests. If you’re considering checking your fertility or undergoing treatment, an antral follicle count is likely in the cards. Many fertility clinics, including IVF Center Hawaii, offer this ultrasound test as part of a comprehensive evaluation. The good news is that knowing your AFC can help you and your healthcare provider make proactive and personalized plans. Whether it’s reassurance that you have time or a nudge to pursue options sooner, the information is empowering. Just remember that a low count is not the end of the road, and a high count isn’t a free pass; every fertility journey is unique.
Sources
- NCBI/Endotext – Ovarian Reserve Testing (2020) – comprehensive review of ovarian reserve markersncbi.nlm.nih.gov
- Cleveland Clinic – “Ovarian Reserve Testing: Range, Purpose & Results” (patient education page)my.clevelandclinic.org