Egg quality does decrease with age, and the decline is one of the most significant biological factors affecting fertility. The change begins gradually in the early 30s, accelerates after 35, and becomes steep after 40. This isn’t just about having fewer eggs. The eggs that remain are increasingly likely to carry chromosomal errors, have less cellular energy, and produce embryos that don’t survive.
What “Egg Quality” Actually Means
When doctors talk about egg quality, they’re referring to whether an egg has the right number of chromosomes and enough energy to be fertilized, divide properly, and develop into a healthy embryo. A high-quality egg completes its final stages of cell division without errors, pairs up its chromosomes correctly, and contains enough fuel to power the first several days of embryonic growth before the placenta takes over.
A poor-quality egg, by contrast, is more likely to have extra or missing chromosomes (a condition called aneuploidy), stall during fertilization, or produce an embryo that stops developing within the first week. This distinction matters because egg quality is the primary reason fertility declines with age, more so than the total number of eggs remaining.
How Sharply Chromosomal Errors Rise
The most measurable aspect of egg quality is the rate of chromosomal abnormalities. In women aged 25 to 30, roughly 25% of eggs are chromosomally abnormal. That number crosses 50% after age 35 and reaches about 88% by age 44. This means that by the mid-40s, fewer than one in eight eggs has the correct chromosome count needed for a healthy pregnancy.
These errors happen during meiosis, the special type of cell division eggs undergo. Proteins called cohesins hold chromosome pairs together so they can separate cleanly. Over time, these proteins degrade. When chromosomes don’t separate properly, the resulting egg ends up with too many or too few chromosomes. Most chromosomally abnormal embryos either fail to implant, miscarry, or in rare cases lead to conditions like Down syndrome.
The Energy Problem Inside Aging Eggs
Eggs are among the most energy-demanding cells in the body. They rely on mitochondria, the tiny power generators inside every cell, to produce the fuel (ATP) needed for fertilization and early embryo development. As eggs age, their mitochondria accumulate damage and become less efficient. They produce less energy and generate more waste in the form of reactive oxygen species, which are unstable molecules that cause further cellular damage.
This creates a vicious cycle: damaged mitochondria produce less energy and more oxidative stress, which damages the mitochondria further. Research has shown that when ATP levels in an egg drop below a critical threshold, fertilization rates fall to less than 30%. The energy deficit can cause an embryo to stall at any point in early development, from fertilization failure to implantation failure to early pregnancy loss.
Oxidative stress also destabilizes the molecular machinery that controls meiosis. This contributes directly to the chromosome separation errors described above, linking the energy problem and the aneuploidy problem into a single age-related cascade.
What This Means for Pregnancy and Miscarriage
The practical consequences of declining egg quality show up clearly in pregnancy outcomes. Miscarriage risk is lowest in women aged 25 to 29, at about 10%. It rises to roughly 17% for women aged 35 to 39, then jumps to 32% for women aged 40 to 44. By age 45 and over, miscarriage risk exceeds 53%. A large Norwegian registry study tracking over 400,000 pregnancies confirmed this steep curve, with the absolute lowest risk occurring around age 27.
IVF data tells a similar story. Cumulative live birth rates per retrieval cycle decline from about 74% for women under 35 to 58% for women 40 and older. These numbers reflect the compounding effect of fewer eggs retrieved, more chromosomally abnormal embryos, and lower implantation rates.
Environmental Factors That Accelerate the Decline
While age is the dominant factor, certain environmental exposures can worsen egg quality beyond what age alone would predict. Bisphenol A (BPA), found in some plastics and food packaging, has been shown to impair embryo development, implantation, and egg quality. Phthalates, another group of chemicals common in plastics, are associated with lower numbers of mature eggs in women undergoing IVF. Endocrine-disrupting chemicals as a class can cause DNA damage and reduce egg quality.
Smoking is another well-established accelerant. Women who smoke tend to reach menopause one to four years earlier than nonsmokers, and their eggs show higher rates of chromosomal abnormalities at any given age. The oxidative stress from cigarette smoke compounds the same mitochondrial damage that aging itself causes.
Can You Test Your Egg Quality?
This is one of the more frustrating aspects of fertility: there’s no simple blood test that directly measures egg quality. The most commonly used marker, Anti-Müllerian Hormone (AMH), primarily reflects egg quantity, meaning how many eggs you have left. An AMH level above 1.1 ng/ml generally indicates a reasonable ovarian reserve, and levels between 1.66 and 4.52 ng/ml are associated with better quality eggs in IVF settings. But AMH is an indirect measure at best.
The only definitive way to assess egg quality is through IVF with preimplantation genetic testing, where embryos are biopsied and checked for chromosomal normality before transfer. For women not pursuing IVF, age itself remains the single most reliable predictor of egg quality. A 38-year-old with excellent AMH levels still has a higher aneuploidy rate than a 28-year-old with lower AMH.
Supplements That May Support Egg Quality
Because mitochondrial dysfunction is central to egg aging, Coenzyme Q10 (CoQ10) has received significant research attention. CoQ10 is a molecule mitochondria use to produce energy, and its levels decline naturally with age. Clinical studies have shown that supplementing with CoQ10 can increase the number of chromosomally normal embryos in older patients and improve embryo quality. Ongoing trials are testing doses of 200 mg three times daily (for the standard form) or 100 mg three times daily (for the more bioavailable ubiquinol form), taken for about three months before egg retrieval.
DHEA, a mild hormone precursor, has also shown promise for women with diminished ovarian reserve. Studies report improved embryo quality, higher pregnancy rates, and lower miscarriage rates with DHEA supplementation, potentially by reducing the rate of chromosomal errors in eggs. One small study found that 100% of DHEA-treated IVF cycles produced at least one chromosomally normal embryo, compared to 53% of control cycles. The effects appear to begin within about two months but peak after four to five months of supplementation, which is why fertility clinics that use it typically start patients at least six weeks before an IVF cycle.
Neither supplement reverses the aging process, but both target the mitochondrial and hormonal pathways most directly involved in egg quality decline.
Egg Freezing and the Age Factor
Egg freezing preserves eggs at the quality they have on the day of retrieval. This is why age at freezing matters enormously. Women who freeze eggs before age 38 have a live birth rate of about 38% per embryo transfer when they return to use them, compared to 29% for women who freeze at 38 or older.
The number of eggs needed for a reasonable chance of success also increases dramatically with age. Mathematical models estimate that to achieve a 75% chance of at least one live birth, a woman would need about 10 frozen eggs at age 34, 20 eggs at age 37, and 61 eggs at age 42. Since most retrieval cycles yield between 8 and 15 eggs, a 42-year-old would likely need multiple rounds of egg freezing, and even then the odds are lower because of the higher aneuploidy rate in each individual egg.
For women considering egg freezing as fertility preservation, the data consistently points to one conclusion: earlier is more effective. The quality advantage of freezing at 33 versus 38 is far greater than the difference a few extra eggs would make.