What Are Ovarian Follicles?

Ovarian follicle is the medical name for an egg sac. Found in the ovaries, these follicles are small sacs of fluid that hold a developing egg. They’re also responsible for secreting hormones that prompt different stages of the menstrual cycle.

Each month, as part of an individual’s menstrual cycle, a select number of ovarian follicles are chosen to grow and develop. However, only one of those selected follicles actually makes it to maturity, with the remainder disintegrating. Once the chosen follicle has fully matured and reached the appropriate size, it bursts, releasing an egg that’s ready for fertilization. The release of the egg usually happens around day 14 of the menstrual cycle, but can vary depending on the length of a person’s cycle. If you’re trying to track your ovulation

What Is the Antral Follicle Count Test?
Antral follicles are the resting follicles present at the beginning of a menstrual cycle that can be seen and counted via ultrasound. An antral follicle count test is a test conducted through a transvaginal ultrasound scan to determine the number of antral follicles an individual has. This count can indicate how many eggs are left in each of the ovaries.

An antral follicle test is “the best predictor of outcome in the context of fertility treatment,”What Size Follicles Are Needed for Fertility Treatments?
Outside of the number of follicles, it’s also important to assess follicle size, as this is an indication of the maturity of the egg in the follicle. In a fertility cycle, the ideal size is between 18 and 22 millimeters in diameter.

Once a follicle reaches this size, it means estrogen levels are rising and the uterine lining has thickened. At this point in a medicated cycle, an injection of HCG or Lupron (depending on what treatment you’re undergoing) is typically administered to spur the final stages of the egg’s maturation.