Egg Health & Fertility
It is important to understand the basics of egg maturation in order to understand why egg health matters and the science behind how you can improve it. SPOILER ALERT: egg quality matters more than egg quantity.
The prevailing belief is that you are born with all of the eggs that you will ever have, but there's more to this story
They were formed during the first half of your mother’s pregnancy with you. At birth, it is estimated that you have ~1-2 M follicles in total. This number can vary widely between women, which is why some women suffer from genetically mediated premature ovarian failure (they were born with a low egg supply and it dwindles quickly; you can also have POF from environmental factors but that’s a separate discussion). Each follicle contains an immature egg. By the time of your first period, it is estimated that you have ~400K follicles left. Full development takes over a year and many stages (Primordial - dormant >> Primary >> Secondary >> Tertiary >> Pre-ovulatory). During each stage of development, only some follicles are recruited to continue to the next stage. The rest die. These follicles compete which each other for about a week, until one starts to outgrow the others. The follicles that aren’t selected for ovulation die (a process called atresia). Because of this, ~1,000 eggs die each month.
Follicles and their potential for eggs
Each follicle has the potential to release an egg during ovulation, but only about 450-500 will actually reach this stage in your lifetime (or ~35-40 years of menstruation, not accounting for pregnancies). The average age of menarche is 12.5 and the average age of menopause is 51…though it can range from 48-55 for most women.
Primordial eggs are like “sleeping beauties”
Eggs in the primordial (dormant) state are not really aware of or affected by what’s going on around them. It’s really once your eggs exit the primordial stage that they start being impacted by your lifestyle, and in particular, in the final one year prior to ovulation. So, this is why your habits and lifestyle really matter when it comes to egg health. Once your eggs “wake up” from their primordial state and begin to mature, they are vulnerable to environmental assaults.
As you age, both your quantity and quality of eggs changes
Quantity AKA “ovarian reserve”: we currently BELIEVE that we are born with all of the eggs we will ever have (though there is some emerging science that suggests otherwise). At this point, I am going to work from that assumption since those are the practical constraints we are working with today.
From this pool of total eggs, many of them are shed consistently each month so our overall quantity of eggs steadily declines over time.
Quality: There are a few parameters that determine egg quality. But the first thing that has to go right for an egg to even have the potential of being fertilized and going on to lead to a viable pregnancy, is that the DNA/genetic material within the egg has to be normal. And there is no spectrum here – it’s binary. The cell either has the correct number of chromosomes or it doesn’t.
Eggs that contain the wrong number of chromosomes either result in failure to get pregnant at all or an increased likelihood of early miscarriage.
As you age, both your quantity and quality of eggs changes. When you are younger, you have a high percentage of eggs that are chromosomally normal. As you get older, you have fewer eggs and a lower percentage of those eggs are chromosomally normal.
But whether or not the egg has the correct amount of genetic material is only step 1. To lead to a viable pregnancy an egg with such normal chromosomes must then survive fertilization, implant, and drive embryo development.
What is the common denominator to all of these processes? A growing body of evidence argues that it is the ability of the egg to produce the energy to fuel these processes that underlies egg quality and health.
What matters is more than just your chronological age
Chronological age refers to the actual time that you have been alive, while biological age refers to how old your body’s systems are.
I’m sure you have seen this disparity in everyday life - the fit, triathlon competing mom who you just found out is in her late 50’s and the graying, saggy-skinned co-worker who you just found out is in her early 30’s. Clearly, we can see that people age at different rates; and it’s probably not surprising that people with “harder” lifestyles (e.g., smoking, drinking, drugs) tend to age more quickly than those with “gentler” lifestyles (e.g., vegetable gardens and Kum ba yah circles).
So, rather than looking at just your chronological age, you can look at a variety of factors to determine your biological age (which is a proxy for overall health): blood pressure, blood glucose, liver function, VO2 max, cognitive ability and so on to determine health status.
The reason I’m even mentioning this is because age has been such a hot button issue in fertility.
I want you to know that it’s not simply your chronological age that matters. The way you take care of yourself matters - the way you eat, move, relax, relate and sleep; these are the inputs...and the output is your overall health status.