Reviewed By: Dr. Sowmya Varudu, fertility specialist at Ferty9 Fertility Clinic, Rajahmundry
In a woman’s lifetime, supply of eggs known as her ovarian reserve, is established before birth and it gradually decreases throughout her life, unlike sperm, which are continuously produced in men. Understanding this natural process is very important to know female fertility at different stages.
Egg count at different stages of woman
Primordial germ cells (PGCs), the precursors of eggs and sperm, emerge outside the developing embryo around the 5th week of pregnancy. They migrate to the genital ridge, which eventually develops into gonads (ovaries or testes). The absence of the Y chromosome determines whether these primordial cells become part of ovaries or testes.
At 20 weeks of gestation (while still in her mother’s womb), a female fetus has the highest number of eggs, estimated to be six to seven million. However, causing a significant decrease in ovarian reserve to one million primary oocytes, which is the total number of eggs a baby girl will have at the time of birth. The SRY gene, located on the Y chromosome, is crucial for determining a baby’s sex, specifically in the development of testes, not ovaries. Females lack the SRY gene, leading to a default pathway for undifferentiated gonads in the developing fetus. The SRY gene does not directly participate in egg formation within ovaries, as the process is governed by other genes and hormonal signals in a female fetus.
This initial reserve continues to decline throughout a woman’s life, even before she starts menstruating.
Puberty: By the time a girl reaches her puberty and begins her menstrual cycles, her ovarian reserve has further reduced to around 300,000 to 500,000 number of eggs.
Reproductive Years: In each menstrual cycle, multiple follicles begin to mature, but only one (sometimes more, leading to twins or multiples) will release an egg during the ovulation. The remaining follicles will degenerate. Over a woman’s reproductive lifespan, which is from puberty to menopause, only about 300 to 500 of her eggs will actually mature and be ovulated.
At the time of Menopause: As a woman enters her late 30s and early 40s, the rate of follicular loss will increase rapidly. The quality of the remaining eggs also tends to decrease. Before menopause is the transitional period leading to menopause. This stage is associated with hormonal fluctuations and changes in menstrual cycles. Menopause is officially reached when a woman has gone 12 consecutive months without a period, generally occur around the age of 50-52 in India. By this time, the ovarian reserve is significantly depleted, with very few viable eggs remaining, often less than 1,000.
Factors Affecting Ovarian Reserve
While the primary factor determining a woman’s egg count is her age, other factors can also potentially impact the rate of decline:
- Genetics: Family history of early menopause might suggest a lower initial reserve or a faster rate of decline.
- Medical Treatments: Chemotherapy and radiation therapy can damage the ovaries and significantly reduce the egg count.
- Ovarian Surgery: Procedures involving the ovaries, such as cyst removal, can sometimes lead to a loss of ovarian tissue and follicles.
- Smoking: Sometimes smoking and alcohol may also be the reason for the depletion of egg count.
- Severe Pelvic Infections: Infections like pelvic inflammatory disease (PID) can potentially damage the ovaries and fallopian tubes.
- Autoimmune Diseases: Certain autoimmune conditions may be associated with a faster decline in ovarian reserve.
How does the count of eggs available impact fertility of woman?
The number of eggs available in a woman’s ovarian reserve is a significant factor in her fertility, and directly impact her chances of conceiving both naturally and through assisted reproductive technologies (ART) like IVF. Here’s a breakdown of how it affects fertility:
(A) Chances of conception:
- Lower Ovarian Reserve (presence of few eggs).
- Reduces natural fertilization opportunities.
- Decline of egg count leads low quality eggs available for fertilization.
- Less likely to fertilize and develop healthy embryos.
- Longer conception time is required for women with lower egg count.
(B) Response to Fertility Treatments:
- Ovulation Induction: Women with a lower ovarian reserve often produce fewer eggs in response to these medications, resulting in fewer eggs available for fertilization.
- In Vitro Fertilization (IVF): IVF involves retrieving eggs from the ovaries, fertilizing them in a lab, and then transferring the resulting embryos to the uterus. A lower ovarian reserve typically means fewer eggs are retrieved, which can lead to fewer embryos available which leads to a challenging situation for quality and also implantation.
- Success Rates: Generally, women with a diminished ovarian reserve may have lower success rates with IVF compared to women of the same age with a normal reserve. This is due to the lower number of eggs available for retrieval.
(C) Risk of Miscarriage and Chromosomal Abnormalities:
- Increased Risk: Lower egg count, may be often associated with a decline in the ovarian reserve. This can increase the risk of genetic abnormalities in the embryos, which in turn raises the likelihood of miscarriage.
(D) Time Sensitivity:
- Accelerated Decline: The decline in ovarian reserve will be rapid as women age increase, particularly after the mid-30s. For women with an already low reserve, this decline can lead to a less opportunity for successful conception.
Conclusion:
The ovarian reserve, established before birth, gradually decreases throughout a woman’s life. By puberty, the reserve is reduced to 300,000 to 500,000 eggs. In Menopause, egg count will be decreasing leading to fewer chances of conception. Factors affecting egg count include age, genetics, medical treatments, ovarian surgery, smoking, and autoimmune diseases. Understanding these factors is very important for understanding female fertility at different stages.
