Glossary · Definition · v2026.3
Ovarian Follicles in IVF
A follicle is a fluid-filled structure in the ovary that contains a developing oocyte. During IVF stimulation, multiple follicles are recruited to grow simultaneously. Not every follicle contains a retrievable, mature oocyte.
Follicles in IVF Stimulation
Antral follicles visible on ultrasound at the start of a cycle represent the recruitable pool for that cycle. During stimulation, FSH-containing medications drive multiple follicles to grow. Follicle size is monitored via ultrasound every 2 to 3 days. When lead follicles reach approximately 17 to 20 mm, the trigger injection is administered. Not all follicles will contain a mature egg; some may be empty or contain immature oocytes.
Biological Constraints
The number of antral follicles declines with age and reflects ovarian reserve. Antral follicle count (AFC) measured by ultrasound and AMH blood levels are the primary predictors of stimulation response. Follicle count sets an upper bound on potential egg yield but does not predict egg quality or chromosomal competence.
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This content defines terminology for educational orientation. It does not constitute medical advice.
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