Flying solo, part 2: “How healthy are my eggs?”
This post is the second in a series and will focus on a topic that is getting a lot of media attention and that is at the forefront of many young women’s minds: egg freezing.
“How healthy are my eggs?” This is one of the most common questions we get asked as fertility docs. Most women are acutely aware that female fertility decreases with age. However, it can be very confusing to see celebrities in their 40s and even 50s getting pregnant, seemingly with ease!
The reality is that many women over 43 who get pregnant are doing it with intensive fertility treatment or egg donation. No matter how healthy we keep our minds and bodies as women, we have limited control of our fertility.
The main reason for the decline in female fertility with age is a reduction in the quantity and quality of a woman’s eggs over time. Typically, a woman is born with 1 to 2 million eggs in her ovaries. From then, there is a gradual attrition, or loss, of these eggs. By the time she hits puberty, many of these eggs have undergone cell death, and only around 300,000 remain.
Through her reproductive lifetime, only 400 eggs will be ovulated or released from the ovaries. By the time she reaches menopause, fewer than 1000 eggs will remain in the ovaries, and pregnancy will no longer be possible.
Along with egg quantity, egg quality also diminishes with time. One aspect of quality that declines is the genetic normality of the eggs. By age 40, over 50% of a woman’s eggs have acquired abnormalities in the chromosomes that carry genetic information. Another issue is that eggs contain cellular organs called mitochondria, which are crucial for generating energy.
As eggs age, the number of healthy mitochondria they contain also decreases. With the quality of eggs declining, even if a woman is ovulating every month, her eggs might not be healthy enough to lead to a successful pregnancy.
So, how do we test eggs?
First, there is no diagnostic test that measures egg quality before undergoing fertility treatment. The only way to examine the eggs is by going through in vitro fertilization (IVF) and seeing how well the eggs develop in the laboratory and whether they result in a successful pregnancy. Short of doing IVF, the only indicator of egg quality is a woman’s age.
In terms of egg quantity, there are two main ways to measure this. The first is called an antral follicle count. This is measured around day 3 of a woman’s cycle and involves an internal ultrasound of the ovaries to count the number of visible fluid-filled sacs that contain eggs (called antral follicles).
The other way is a blood test that measures the anti-mullerian hormone (AMH) level. AMH is a hormone made exclusively in a woman’s egg follicles, and its level in the blood is a reflection of the number of eggs she has. Taken together, these two tests help us estimate a woman’s egg supply.
One important thing to note is that how many or how few eggs a woman has does not always predict natural fertility. Egg supply alone is not enough to predict whether a woman can conceive. Some women have a relatively low egg supply but have no difficulty getting pregnant naturally!
However, testing egg supply is important for women who are experiencing difficulty conceiving. These tests tell us whether a woman’s egg supply is declining and how urgently she might need to consider doing fertility treatment. It also helps us predict how many eggs a woman might be able to produce during fertility treatment and how likely it is that treatment will succeed.
The bottom line is that testing egg supply is a good idea if a woman wishes to learn more about her fertility options or is contemplating fertility treatment. But the results need to be discussed with a fertility specialist to accurately interpret the findings for her individual situation.