Understanding Your Ovulation and Ovarian Reserve

When you start thinking about trying to conceive, one of the first things you need to learn about is “ovulation”.  Women’s Health Nurse Practitioner Tamara Tobias explains everything you need to know about ovulation and ovarian reserve:

The menstrual cycle consists of a pre-ovulation (follicular) phase and post-ovulation (luteal) phase. Follicular refers to when a follicle (fluid surrounding the egg) is growing and getting ready to ovulate.

Ovulation can often be predicted with ovulation predictor kits (OPKs), which detect the luteinizing hormone (LH) surge prior to ovulation. Since progesterone increases after ovulation, a progesterone blood test one week after a presumed ovulation can also be used to confirm if ovulation indeed occurred.

If you get your period on a regular pattern every month, then you are likely ovulating. However, if your cycles are longer, like every 35-40 days, then you may have times when you are not ovulating. Oral ovulation medications can be used to overcome this irregularity. It is also important to let your provider know if you experience any abnormalities such as spotting in-between your periods or significant discomfort during your period or with intercourse.

Ovarian reserve refers to your egg supply and helps us predict how you may respond to fertility medications. I think it is fascinating that as women we are born with all of the eggs we will ever have yet, unfortunately, we cannot make more eggs. Tests to check your egg supply or ovarian reserve may include:

• Cycle day 3 FSH (Follicle Stimulating Hormone) and estradiol level
• Antimullerian Hormone level (AMH)
• Antral Follicle Count (AFC) ultrasound

The FSH and estradiol blood tests are performed on day 2, 3, or 4 of your menstrual cycle. This blood test is done on the first days of your period because that is when your ovaries are normally quiet (not growing an egg), and your estrogen is low. FSH from your pituitary will then stimulate a follicle (egg) to grow. As we get older, the eggs become more difficult to stimulate, which results in a rise of FSH. An elevated FSH level is an indicator of decreasing egg supply or ovarian reserve and high FSH levels are used in the diagnosis of menopause. Estradiol is important as well because if the estradiol level is elevated, it can cause the FSH level to look incorrectly low. Therefore, you really need both a FSH and estradiol level to assess ovarian reserve. Sometimes the estradiol level may be high because a follicle is already starting to grow. The increased FSH level stimulates earlier onset of follicular growth and can result in short menstrual cycles; another indicator of diminished ovarian reserve.

Antimullerian hormone (AMH) is a hormone produced by cells that are in the small growing follicles, even the microscopic ones that we cannot see on ultrasound. This level decreases with age as the egg supply continues to deplete. This blood test may be done any time during your menstrual cycle and even if you are on birth control pills. However, long term use of birth control pills could suppress the AMH level and your provider may recommend discontinuation of them for 1 month and then repeat your AMH level if your first level was abnormally low.

The antral follicle count (AFC) is determined with a transvaginal ultrasound, which can be performed anytime during the menstrual cycle. The antral follicles are the small follicles seen on ultrasound, which I call “little wannabes.” These antral follicles can be counted and the total number reflects your egg supply. See my illustration below. The average AFC is between 10-25 follicles total (both ovaries, not each one).

*Note: this illustration is an average. The quality of eggs diminishes with age, but the number of follicles is variable for every woman. A younger woman may have a lower number of antral follicles but the quality is still good versus an older woman with a high number of eggs but poor egg quality.

Age also plays a significant role with regards to fertility. As a woman gets older, her egg supply diminishes, and there are no medications that can increase egg supply. A mature egg must also divide its chromosomes in half in order to be fertilized. As we age, that process of dividing does not work as well and may result in chromosomal abnormalities. This explains why the miscarriage rate and risks of Down syndrome go up as we get older.

*These two ultrasound images demonstrate normal ovarian reserve. The ovary size is appropriate; 12 follicles were counted on the right ovary, and 13 follicles were counted on the left ovary, totaling AFC of 25 follicles.

*These ultrasound images demonstrate significant decrease in ovarian reserve. Often, the ovary may be smaller in size. Note that there is only 1 small black dot (antral follicle) noted on each ovary. This indicates that the egg supply is very low, so response of ovarian stimulation may be limited.