Many women believe that how many eggs they have left—their egg count—is the primary indicator of their fertility. But, while egg count is part of the equation, the true driver of fertility is egg quality, and the decline in egg quality is a natural, inevitable result of age.
Here’s what you need to know about fertility and egg quality:
Declining egg quality and fertility comes naturally with age.
You’ve probably heard this before, but let us reiterate: Women are born with all the eggs they’ll ever have, typically 1–2 million. Over time, that healthy egg supply decreases in two ways. First, women lose eggs each month—about a thousand a month after puberty—and by age 35 have only about 6% of their remaining egg count.
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Secondly, with age there’s a decrease in egg quality, which is a bit more complex. You’re born with all your eggs, but for most of your life, they remain dormant in your ovaries in their immature, “primordial” form. That is, until they’re called to action during a particular month—the month they’ll potentially be ovulated. Just before ovulation, these eggs go through a process of maturation, including cell division (called meiosis). Older eggs are more prone to errors during this division process; that’s why it’s more likely that older eggs, once ovulated, will contain abnormal DNA. If you remember back to high school science, DNA is what tells a cell to do what it needs to do. So without healthy DNA, an egg can’t perform its function: make a healthy baby. And as you age, more of your eggs become unhealthy.
Your other eggs remain tucked away inside your ovaries, affected by the aging process (we don’t know exactly how), but generally unaffected by the majority of the wear and tear the rest of your body weathers. This has pros and cons: while your egg health doesn’t seem to be meaningfully impacted by the cumulative influence of everyday toxins or illness, it’s also not meaningfully improved by antioxidants, supplements, or nutrients that might support healthy cells in other parts of the body.
All women have some percentage of abnormal eggs. According to studies of embryos created from eggs of different ages, women in their early 20s have about 20% abnormal eggs, while women in their 40s have upwards of 80% abnormal eggs. This decline in egg quality and fertility is seen across populations.
Most eggs with abnormal DNA, also known as “aneuploidy,” don’t fertilize at all, hence the relationship between fertility and egg quality. A small percentage may fertilize, but result in miscarriage, and an even smaller percentage may result in genetic disorders for the baby, such as Down syndrome. Declining egg quality is why we see miscarriage and Down syndrome at much higher rates in women over 35.
Fertility is driven by egg quality.
Okay, so both egg count and egg quality affect your fertility—but egg quality is really the boss here.
Think of your fertility as a gumball machine. Each month in a natural menstrual cycle, your body withdraws one gumball (egg) from the machine (your ovaries). That egg is either healthy or unhealthy. As you age, you have fewer gumballs in the machine, and a higher percentage of the gumballs are unhealthy, lowering the chances that the one you get in a given month will be able to result in a healthy baby. That’s why it can take much longer—many more menstrual cycles—for older women to get pregnant.
Even when fertility medicine comes into play, the relationship between age, fertility, and egg quality affects chances of success. Fertility treatments like in vitro fertilization use hormone medications to prompt the ovaries to produce multiple eggs in one cycle, but some of those eggs will still be abnormal (how many are abnormal will depend on your age). So while IVF can help increase the chances of finding some healthy eggs, it can’t make more of your eggs healthy. If a woman in her 40s retrieves 10 eggs in an IVF cycle, it’s likely that only 10–20% of those eggs will be normal. If she retrieves 20 eggs in two IVF cycles, still only 10–20% of those eggs will be normal—but she’ll have more to work with because she retrieved more.
That’s why we see declining success rates as women age, even when using advanced reproductive technology like IVF. If there are very few healthy eggs to work with, the chance of success is low.
There’s no fertility test for egg quality.
The fertility testing that exists, often called ovarian reserve testing, tests for markers of your egg count, not your egg quality. Fertility tests, like anti-Müllerian hormone levels, tell you how many eggs you have left, which can help predict how many eggs you’ll be able to retrieve during an egg freezing or IVF cycle. This is important info—but it’s only part of the picture.
The only way to know for sure if an egg is chromosomally normal is to attempt to fertilize it, and, if fertilization is successful, to perform a genetic test on the embryo; the egg quality of an unfertilized egg, which is only a single cell, can’t be safely tested with current medical technology. However, because errors in our eggs’ DNA happens naturally and inevitably over time, and because the impact of age on egg quality is consistent and universal, your age can give doctors a very accurate picture of what percentage of your eggs are normal.
That’s why a fertility assessment and consultation here at Extend Fertility includes not only a blood test and an ultrasound, but a conversation with a doctor, who can help you understand your individual fertility test results, your predicted egg yield, and your chance of success with egg freezing.
There’s not much you can do when it comes to improving your egg quality.
Egg quality is not a scale of healthy to unhealthy, with measures in between—it’s a binary state of either normal or abnormal. Once an egg divides with abnormal DNA, it can’t be fixed medically or “healed.” In other words, once an egg becomes abnormal, it can’t become normal again.
The decline in egg quality is driven solely by age, with a few exceptions. Women who smoke cigarettes typically have fewer eggs and a lower percentage of healthy eggs, and go into menopause an average of four years earlier than women who don’t smoke cigarettes. According to ASRM, female smokers going through IVF have 30% lower pregnancy rates than patients who don’t smoke.
Egg quality can also be affected by exposure to systemic, toxic medications, like the chemotherapy drugs used in treatment for cancer. Obviously, while smoking is completely preventable, cancer treatment is not something you’d forgo for the sake of your eggs. That’s why many women freeze their eggs before cancer treatment.
Lastly, egg quality and overall fertility may be affected by other reproductive illnesses, such as endometriosis. Studies (1, 2) demonstrate that women with endometriosis have fairly high pregnancy rates when they undergo IVF with eggs donated by a woman without endometriosis. But when it’s the other way around—when women without endometriosis do IVF using donor eggs from women with endometriosis—success rates are “significantly reduced,” leading experts to believe endometriosis may affect egg quality.
There’s no evidence that specific diets, herbal treatments, acupuncture, yoga, massage, or other alternative therapies can improve fertility and egg quality. The majority of the nutrients that people often associate with fertility, such as folic acid, are really only helpful for women who are currently trying to conceive, because they support the developing fetus—but they don’t have any effect on the eggs inside your ovaries.
While some alternative therapies like massage and yoga can help women feel more relaxed during an IVF or egg freezing cycle (and mental health is really important!), we caution that women shouldn’t rely on them to significantly improve success rates, and shouldn’t be swayed by marketing that presents these treatments as “natural fertility solutions.” We wish it was that easy, but the scientific support just isn’t there—there’s no “anti-aging” treatment for your eggs.
Learn more about alternative medicine and fertility.
The only way to preserve your egg quality and fertility is through cryopreservation (freezing).
Cryopreservation, such as egg freezing, is the only technique that currently exists to extend your fertility. Eggs that are retrieved from the body and cryopreserved don’t become damaged with age like the eggs in your body, so their health is essentially frozen in time—giving you the ability to use those healthy eggs for a pregnancy later on, when your natural fertility and egg quality has declined.