All the eggs a woman will ever have are created in the first 16 weeks while they are still inside their mother’s womb. Approximately 4 to 5 million eggs are formed but only 1 to 2 million eggs remain at the time of birth. Of these, only 400 000 to 500 000 are still viable at puberty. Up until the menopause, a woman is expected to ovulate 400 to 440 times.
In essence, human eggs are “destined to die”.
Menopause generally occurs when there are less than 1000 eggs left in the ovaries. On average, this occurs at about age 54 years. Women who have experienced endometriosis go through menopause at an average age of 49 years. Premature menopause can occur before the age of 40 years and is often genetically linked. Other conditions such as Fragile X syndrome can also result in premature menopause.
Any woman less than 35 years old who has been trying to conceive without success for more than 12 months should seek help. If over 35 years old, a woman should seek help if unsuccessful after 6 months of trying to conceive. One of the first things a fertility specialist will check is your ovarian reserve (egg supply).
Factors that Affect Egg Quantity and Quality
Age is the most important factor affecting egg supply and quality. Women are born with a finite number of eggs and quality deteriorates with age. But, even older women will have good quality eggs; they just have less of them.
Endometriosis can decrease egg numbers and quality. If endometriosis involves the ovaries and surgery is required, this can further reduce egg numbers. Egg quality tends to improve after excision of endometriosis.
3. Polycystic ovarian syndrome
In this condition, women do not have more eggs than other women. They have more eggs coming out of “stasis” each month. Within any group of eggs, there are a normal number of good quality eggs but a higher number of poor quality eggs. In those requiring IVF, the number of eggs retrieved equates to a higher chance of pregnancy. It is just a matter of finding the “good eggs”.
4. Other medical conditions
There are many conditions that can affect number and/or quality of eggs. Thankfully, these are rare, but with treatment, most women can achieve a pregnancy. Conditions include cancer and its treatments, autoimmune disorders, premature menopause, chromosomal abnormalities, fragile X syndrome and ovarian surgery.