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Dominant Follicle

Last Updated: March 21, 2020

Definition - What does Dominant Follicle mean?

A dominant follicle is a fluid-filled structure in the ovary that grows big enough to release a mature egg around day 14 of a 28-day menstrual cycle or around a week prior to the midpoint of a cycle through the process of ovulation.

A dominant follicle is also called a Graafian follicle.

FertilitySmarts explains Dominant Follicle

Before puberty, an ovary contains thousands of follicles, called primordial follicles. With the onset of puberty, 15-20 primordial follicles begin to mature each cycle. This process is referred to as follicular recruitment. Only one of the 15-20 recruited follicles becomes a dominant follicle, which is capable of expanding and releasing a mature egg.

The cells in the dominant follicle produce estrogen. The rest of the follicles shrivel up and die. When the dominant follicle reaches 2 to 4 cm in diameter, it bursts to release the egg, marking the onset of ovulation. After ovulation, the dominant follicle partially shrivels and is now called the corpus luteum and produces progesterone during the last phases of the menstrual cycle.

What triggers the formation of a dominant follicle? When a menstrual cycle begins, a part of the brain called the hypothalamus releases gonadotropin-releasing hormone (GnRH). GnRH acts on the pituitary gland, which in turn secretes follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones trigger the maturation of the recruited follicles and eventually the formation of a dominant follicle.

During fertility treatments like in Vitro fertilization (IVF) or intrauterine insemination (UI), ovarian stimulation helps more of the recruited follicles to mature by using high concentrations of FSH, as opposed to the natural development of a single dominant follicle during a typical menstrual cycle.


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