The simple answer: an egg’s capability to turn into a baby. (With the help of sperm, of course!)
The complex answer: while there is no ONE true test for egg quality, there are several factors that give us an idea.
- Is the egg producing adequate hormones?
- A growing follicle (like the shell around the egg) is what MAKES estrogen. If estrogen is low, the follicle is not functioning very well, and usually indicates a low quality egg inside. This is true for progesterone as well.
- Is the diagnosis “unexplained infertility,” or “advanced age?” In lieu of other identifiable diagnoses, we can guess that egg quality may be playing a role in infertility.
- Is AMH and antral follicle count low? These are not direct measures of quality, but rather quantity. However, it is now thought that AMH may show some reflection of quality as well.
- Is the egg able to be fertilized?
- This is more obvious in the context of IVF, where we can watch and count fertilization happen before our eyes. Average fertilization rates are 70-85%.
- If fertilization rates are lower than that, it could be egg OR sperm OR both.
- Can the fertilized egg develop into a day 5 blastocyst? On average, 30-50% can make it to day 5. That broad range, and anything outside of it, may have clues to egg quality.
- What is the “grading” of that embryo/blast? The embryology lab will give each embryo a score based on factors like it’s appearance, development, and maturity. While this may again speak to either egg OR sperm health, we look at the final embryo as a reflection of the initial ingredients.
Most of what we know about egg quality is uncovered through IVF. Up until that point, we’re guessing.
Research is starting to tip the scales about things that can support or harm egg quality. New technology is trying to find a way to test or quantify egg quality. One day we may have more answers, so for now we look at the list above for clues.