As eggs, or Oocytes, are microscopic, you cannot really determine how many you have. However, the immature egg cells secrete a hormone call AMH (anti-Mullerian hormone) which can be measured and interpreted in the context of what is the average measure of this hormone for one’s age group.
Females are born with a finite number of eggs, and oddly, egg cells do not replicate or renew like all other cells in the body. Egg cells, or Oocytes, rest in a dormant state in the dense ovarian tissue until they one day respond to FSH from the pituitary and start the process of maturation, and possibly, successfully ovulate. Each month, regardless of age, hormonal use, pregnancy, etc., there is a small group of eggs that starts the process of maturation but then regresses, and this group is absorbed by the body. This is called programmed cell death or apoptosis. This is the main reason for the depletion of the ovarian reserve for all women over time. A woman may ovulate 500 eggs in her lifetime, but the majority of the 1-3 million eggs she is born with undergo apoptosis and are not utilized for fertility.
Ovarian reserve is quite variable at any age, but generally more abundant at a younger age. There is a wide variety of the number of eggs any individual female has at birth; and a wide variety of the rates of apoptosis.
There could be a Nobel prize waiting for the scientist who discovers how to suspend or slow the process of apoptosis!
Then there are environmental factors that can diminish ovarian reserve, such as:
In general, an AMH of 2 or above is associated with a normal response to the medications used for fertility, particularly for preparation for an IVF or Egg Freeze cycle. An AMH under 1 can make it difficult, although still possible, to complete an IVF cycle or Egg Freeze cycle.
Interestingly, an AMH all by itself does NOT predict fertility or infertility. There are so many factors involved in the conception, that as long as there is sufficient ovarian reserve for ovulation, the AMH cannot predict who will conceive naturally within one year of trying. Other measures of the ovarian reserve include the Antral Follicle Count, performed with pelvic ultrasound, and the day 2 or day 3 hormones of FSH and Estradiol. Antral Follicles are 2 to 10 mm each and typically hold one immature egg that could proceed towards maturation and ovulation in the upcoming months. The most dormant (primordial) egg cells do not have follicles or fluid sacs and cannot be inferred from ultrasound assessment. The FSH hormone is secreted by the pituitary and serves to recruit a few immature antral follicles into the maturation process. As the egg matures, the cells around the egg secrete estradiol. The pituitary senses the estradiol and decreases the FSH secretion. If the egg maturation is not occurring, the estradiol is not rising, and the pituitary raises the FSH secretion to nudge a follicle to start its maturation. A higher FSH (greater than 12) signals a less responsive ovary and a lower ovarian reserve. The FSH can only be interpreted when the estradiol is normal (less than 65). The AMH level can detect more subtle declines in ovarian reserve. However, the AMH blood test, which can be done any day of the cycle, may be suppressed with long-term pill use.
The greatest utility of all of these ovarian reserve measures, and particularly true of the AMH level, is that this information about ovarian reserve permits an infertility specialist, such as Dr. Moomjy, to best select a hormonal regimen that is most likely to result in an ideal egg yield with the least amount of side effects.
Importantly, estimated ovarian reserve and age are the two factors that can permit better counseling of the patient as to what to expect from anticipated fertility treatment.
“Testing and interpreting measures of ovarian reserve: a committee opinion,” Practice Committee of the American Society of Reproductive Medicine, Fertility and Sterility, Dec 2020 pp 1125-1348.