What Is ‘Normal’ Follicle Size For Ovulation?

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Dr. Rachel Adams Rachel is a board-certified obstetrician-gynecologist who practices at Metropolitan OB-GYN at Mercy Medical Center.
Rachel Adams, M.D. Obstetrics / Gynecology
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During some fertility treatments, your ovarian follicles may be monitored. This includes evaluating the size of your follicles.

Ovarian follicles are small sacs in the ovaries that contain immature eggs. Monitoring them helps doctors gauge how many eggs an individual may have in reserve. This can indicate the odds that a fertility treatment will be successful.

If you’re currently undergoing fertility treatment or planning to in the future, here’s what to know about ovarian follicles including the typical follicle size for ovulation.

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, discuss menstrual tracking with your doctor.

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,” according to Isaac Sasson, M.D., Ph.D., who serves as medical director of Shady Grove Fertility Pennsylvania. In other words, an antral follicle test can help predict the chances of fertility treatment working. As a person ages, they have less antral follicles at the beginning of their cycles.

As such, an antral follicle test is a common component of fertility treatment. “When doing IVF, we need to figure out what dose of drugs to give the patient, and that dosing is based on age, AMH level [a hormone that helps indicate ovarian reserve] and antral follicle count,” explains Thomas Price, M.D., reproductive endocrinology and infertility specialist at Duke Health in Durham, North Carolina.

How Many Antral Follicles Should I Have?

On average, an individual without fertility issues can have anywhere from five to 17 antral follicles[1].

However, the specific number of antral follicles varies from person to person, depending on an individual’s fertility levels as well as their age. One study found that whereas the median antral follicle count for individuals with “proven natural fertility” was 13, that median value fell to nine for women with fertility issues[2].

Additionally, the older a person gets, the fewer antral follicles they will generally have. According to Dr. Sasson, while a person in their 20s can have as many as 20 follicles each month, that number may fall to 15 for a person who is 35, and then around eight to 10 at age 40. By menopause, a person’s follicles are depleted[3].

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.

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Can I Still Get Pregnant With a Low Follicle Count?

A low follicle count by no means rules out the possibility that someone can get pregnant. Rather, follicle count is “more of an indicator of how many eggs someone is going to make with injectable fertility drugs,” says Dr. Price.

Still, a low count does mean that if someone were to come in to get fertility treatment, they’ll likely get fewer eggs. “It might take more tries [to get pregnant],” says Dr. Sasson. “It’s more like winning the church raffle — the greater the number of tickets you have, the greater chance you have of winning the raffle.”

There are many options available for those seeking fertility treatment and a low follicle count does not mean you will never become pregnant. Reach out to your doctor for support and to find out what steps you should be taking to further your reproductive goals and remember––you are never alone.

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