Understanding Human Eggs

Understanding Human Eggs

human eggs

By Dr Andy Stamatiou, Specialist at City Fertility Centre Brisbane

You will have a better understanding of fertility by understanding human eggs. Did you know that all the eggs a woman will ever have, are created in the first 16 weeks while she is in her mother’s womb?

Approximately four to five million eggs are formed in those first 16 weeks, but only one to two million eggs remain at the time of birth. Of these, only 400 000 to 500 000 are still viable at puberty.  In essence, human eggs are “destined to die”.

Up until the menopause, a woman ovulates (releases eggs) about 400 to 440 times. Menopause occurs at an average age of 54 years, when there are less than 1000 eggs left in the ovaries. Women who have experienced endometriosis will go through menopause a little earlier at about 49 years of age. Premature menopause can occur before the age of 40 and is often genetically linked. Other conditions such as Fragile X syndrome can also result in premature menopause.

My recommendation is that women less than 35 years of age and trying to conceive without success for more than 12 months should seek help. If they are over 35 years, they should seek help when no pregnancy occurs after 6 months of trying. One of the first things a fertility specialist will check is your ovarian reserve (egg supply) as this can often be a factor when having trouble conceiving.

Here is some more information about what affects human eggs, how to test egg supply, and the treatment options available, if required.

Factors That Affect egg Quantity and Quality

  • Age: This is the most important factor affecting egg supply and quality. As already mentioned, women are born with a finite number of eggs with quality deteriorating with age. Yet, even older women can have good quality eggs; they just have less of them.
  • Endometriosis: It 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.
  • Polycystic ovarian syndrome (PCOS) –With PCOS, women do not have more eggs than other women. However, they do have more eggs coming out of dormancy each month. Despite this, ovulation occurs sporadically or not at all. 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”.
  • 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.

Methods for Testing egg Supply

There are three commonly performed tests which give useful information about egg numbers in a woman.

  • Anti-Müllerian Hormone (AMH)

The AMH is a very useful test. It tends to decrease with age as egg numbers decrease. It can often point towards common causes of infertility. A lower than expected AMH level raises concerns about endometriosis and other rarer causes of decreased egg numbers. A higher than expected level, points towards the possibility of polycystic ovarian trait/syndrome. When fertility treatments are required, the AMH serves as a guide to the dosage of medications used.

An AMH is often done to give reassurance to women who want to delay child-bearing. For example, women who do not have a partner or women whose careers depend on them continuing to work. Delaying child-bearing until after age 35 years, is not recommended, as egg quality plays a major part in the chance of success. If a woman can foresee that she will not plan to start a family until after age 35, she should consider egg freezing at a younger age. The AMH is not a good predictor of when menopause will occur.

The test for AMH is a simple blood test that can be done at any time of the menstrual cycle but not immediately after ceasing the oral contraceptive pill. In Australia, the test costs approximately $75 to $85. There is no Medicare rebate.

  • Follicle-Stimulating Hormone (FSH)

The FSH is a simple blood test ideally done on day three of the menstrual cycle, but can be done from days two to five. It is performed as a routine for anyone being investigated for infertility and has a Medicare rebate.

The FSH begins to rise as egg numbers dwindle and reaches a peak with the onset of menopause. The majority of women with low egg numbers have a relatively normal FSH.

  • Antral Follicle Count (AFC)

This test is done with the use of a transvaginal ultrasound scan from day one to day five of the menstrual cycle. It counts the number of small follicles in the ovaries. A certain number of eggs come out of stasis each month and have potential to grow. It is assumed that each follicle contains an egg.

In women with low egg numbers, the AFC can vary month to month. This test can be used to decide on which month to start an IVF cycle.

When investigating egg supply, your fertility specialist will look at the results of all three tests to get an overall picture of your ovarian reserve.

Treatment Options (If Required)

Treatments are available for women with low egg numbers depending on the cause. Options to consider are:

  • Surgery to diagnose and excise endometriosis
  • In-vitro fertilisation (IVF)
  • Donor eggs or donor embryos.
  • Egg freezing is readily available to all women of reproductive age. The advent of new vitrification (snap freezing) techniques has increased success rates for achieving a pregnancy using frozen eggs. The younger eggs are at the time of freezing, the better they are. For example, a woman at age 28 requires 7 eggs on average to achieve one pregnancy, at age 35, 12 eggs are required to achieve one pregnancy. Unfortunately, there are those women who may never achieve a pregnancy despite having good numbers of frozen eggs. These cases often have other causes for infertility that may not be discovered until they come to use the eggs.

Time is of the Essence

I spend time visiting my GP colleagues to make them aware of what we can do to educate women about their reproductive ‘clock’. If you get tested and find you have a low ovarian reserve, see a fertility specialist as soon as possible. The younger you are, the better your chances of future success.

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