Antral Follicle

An antral follicle is a fluid-filled sac containing an immature egg that is developing within a woman’s ovaries. It is called an antral follicle because at this stage the follicle contains a fluid-filled cavity called an antrum.

Antral follicles are larger than follicles at earlier stages of development, so they can be visualized on an ultrasound. Although not all antral follicles will continue to mature and be released during ovulation, the number of antral follicles a woman has in her ovaries is a good indication of how many eggs she has left. A woman with a low antral follicle count may struggle with infertility.

Antral follicles are also called resting follicles.