Human oocyte

When it comes to oocytes (eggs), there are two main defining features: Quality and Quantity. Egg quality most fundamentally refers to the cell’s genetic makeup, where each egg can either be genetically intact/normal or abnormal. Egg quantity, also referred to as ovarian reserve, refers to the approximate number of eggs present in one’s ovaries. Today, the simplest and most accurate way to determine ovarian reserve is through measuring AMH (Anti-Mullerian Hormone) through a blood test. AMH is produced by the ovaries, making it a direct reflection of their reserve.

Before we dive into what the descriptor “diminished” means when referring to ovarian reserve, including its impact on fertility, let’s start with reviewing what ovarian reserve is and how it relates to the biological clock.

Egg Freezing Oocyte Quantity and Quality of Eggs for Younger and Older Women.

What holds true for everyone is that egg quantity as well as quality decreases over time, with natural aging. At Extend we use a gumball machine analogy to illustrate this phenomenon. The gumballs represent eggs, those that are colored white are genetically normal and those colored blue are genetically abnormal. The left gumball machine has more gumballs overall, as well as a higher proportion that are white. The right gumball machine has fewer gumballs overall, as well as a higher proportion that are blue. As you can see, over time women lose egg quantity and of those left, a higher proportion become genetically abnormal.

AMH levels decline over time.

Egg quantity, as reflected in AMH, can vary widely from one woman to another, even of the same age; egg quality, on the other hand, is generally consistent for every woman of the same age. In the chart above, you can see the comparison of the 10th, 50th and 90th percentile of ovarian reserve for women of different ages. What was observed in this study is the large variability in AMH at each age. For example, a 90th percentile 35-year-old will have the same AMH as an “average” (50th percentile) 25-year-old! Conversely, a 10th percentile 30-year-old will have the same AMH as an average (50th percentile) 43-year-old!

While it has been established that women are born with all the eggs they will ever have, current research has not determined the reason behind the individual variability in AMH. The implication then is that nothing can be done to control ovarian reserve, including increasing it. The question that then arises is whether AMH or ovarian reserve impacts natural fecundity, one’s ability to conceive naturally.

The answer is… NO. Let’s get into it!

Ovarian Reserve and Conceiving Naturally

For women of reproductive age, each month one egg is grown to maturity and is ovulated and thereby available for potential fertilization. This happens whether you have a very high or very low ovarian reserve. Additionally, egg quality is the same for all women of the same age, regardless of quantity. If you isolate all other factors impacting fertility (such as fallopian tube health, hormone levels, sperm health, etc.)  and only focus on egg quality and quantity, every woman of the same age has the same chance of conceiving naturally. A study by Steiner, A. et al, focused specifically on biomarkers for ovarian reserve and whether they were also biomarkers for reproductive potential. They found that low ovarian reserve is NOT associated with reduced fertility. As you can see in their results summary chart, women with high variance in AMH all had the same probability of conception at each age.

Probability of conceiving

Why measure ovarian reserve at all?

Ovarian reserve, as reflected in AMH, is incredibly useful for those who use assisted reproductive technology, like IVF and egg/embryo freezing. It gives fertility specialists the ability to predict how many eggs can be retrieved during one stimulation cycle and chances of conceiving with those eggs. This is where diminished ovarian reserve will have bigger implications. A lower AMH means fewer eggs can be harvested with each cycle, leading to a lower chance of conceiving through IVF.

Is diminished ovarian reserve correlated with low egg quality as well?

While diminished reserve is correlated with fewer embryos being created with each IVF cycle due to a lower overall quantity, a study by Morin, S. et al found that the ratio of embryos created to eggs retrieved and the live birth rate per embryo transfer is the same for all women of the same age, regardless of ovarian reserve. The takeaway from this study is that , quality remains the same for women of the same age, even though the quantity can be vastly different.

We leave you on this positive note – whether a woman is in the 10th, 50th or 90th percentile oocyte yield, creating a euploid embryo and achieving pregnancy is possible. For those who wish to have biological children of their own, it can be worth the time, effort, and money to put into trying. This is a conversation you would have at the beginning stages of working with a fertility specialist!