Antral follicles are small, fluid-filled sacs in ovaries, each containing an immature egg. Their fluid-filled cavity, an antrum, makes them visible via ultrasound, marking a specific stage in ovarian follicle development.
Formation and Role in the Ovarian Cycle
Egg development begins with primordial follicles, microscopic and present from birth. Throughout reproductive life, some activate, progressing through primary and secondary stages, culminating in antral follicle formation.
Antral follicles play a role in the follicular phase of the menstrual cycle. Each cycle, a cohort is recruited for maturation. Follicle-stimulating hormone (FSH) stimulates their growth, leading to increasing estrogen secretion.
From this cohort, one dominant follicle is selected to develop and release a mature egg during ovulation. The remaining antral follicles degenerate and are reabsorbed. This process ensures one egg is typically released per cycle, though occasionally more than one can be.
Antral Follicle Count (AFC)
The Antral Follicle Count (AFC) is a non-invasive assessment measuring antral follicles. Performed via transvaginal ultrasound, follicles measuring 2-10 millimeters are counted.
The AFC test is conducted during the early follicular phase of the menstrual cycle, between day 2 and day 5. This timing ensures visibility and measurability. The total count estimates available eggs. This informs about ovarian reserve (the remaining egg supply).
Implications of AFC
The Antral Follicle Count indicates a woman’s ovarian reserve, reflecting her remaining egg pool. A “normal” AFC ranges from 12 to 24 follicles, varying with age and individual factors. A count between 9 and 21 is considered intermediate to normal, suggesting a good response to ovarian stimulation.
A low AFC, below 10 follicles, may suggest diminished ovarian reserve, indicating fewer eggs. This indicates a lower likelihood of responding well to IVF, potentially requiring higher medication doses. Conversely, a high AFC, exceeding 20 or 30 follicles, can be observed in conditions like Polycystic Ovary Syndrome (PCOS). Such cases risk exaggerated response, requiring careful monitoring to prevent ovarian hyperstimulation syndrome.
The AFC is a predictive tool for ovarian response to IVF medications, with higher counts correlating with better response and more eggs retrieved. While age is a significant fertility factor, AFC provides insight into reproductive potential. It helps tailor treatment protocols and estimates success rates in fertility interventions.