Egg Quality and Age: Why It Declines, and What New Research Means for IVF

On 29 October 2026, researchers at Chiba University, Japan, published a study in Nature Aging that sheds new light on one of the most fundamental questions in reproductive medicine: why does egg quality decline with age? The findings were reported in The Times the same evening and have already attracted attention from fertility specialists and researchers worldwide.

For anyone preparing for IVF in their late 30s or 40s, this matters. Egg quality is one of the most significant factors in IVF outcomes, and understanding what is happening at a biological level is the first step to understanding what you can and cannot influence.

This article explains the new research in plain language, what it means for IVF now and in the future, and what steps you can take in the months before treatment to support egg health.

Egg quality and age: what actually changes

A woman is born with all the eggs she will ever have. Unlike sperm, which are produced continuously throughout a man's life, eggs form during foetal development and then enter a long dormant state that can last for decades. By the time an egg is ovulated, it may have been waiting in that suspended state for 30, 40, or even 50 years.

Understanding egg quality and age means understanding two distinct things: egg quantity and egg quality. These are not the same.

• Egg quantity (ovarian reserve) refers to how many eggs remain. This is estimated using AMH levels and antral follicle count, and it declines over time, more quickly from the mid-30s.
• Egg quality refers to the chromosomal and cellular health of individual eggs. This is what most directly affects whether a fertilised egg becomes a viable embryo.

Age affects both, but it is the decline in egg quality, specifically the rising rate of chromosomal errors, that has the greatest impact on IVF outcomes.

Why chromosomes matter so much

Inside each egg, chromosomes must be correctly paired and then separated accurately as the egg completes its final maturation before ovulation. For this to happen, the chromosomes need to be held in precise alignment by a protein complex called cohesin. That supply of cohesin is laid down during foetal development and is never replenished. It simply has to last.

As the years pass, cohesin gradually weakens. The older the egg, the higher the chance that chromosomes will separate incorrectly when the egg matures, producing an egg with too many or too few chromosomes.

The role of mitochondria

Chromosomal integrity is not the only factor. Mitochondria, the energy centres of the egg, also decline in function with age. Eggs require enormous amounts of energy to complete the final stages of maturation, and when mitochondrial output falls, the risk of errors during cell division rises further.

These two processes, weakening cohesin and declining mitochondrial energy, work together to explain why egg quality and age are so closely linked. Egg quality and age also shape egg freezing decisions, which is why timing matters so much for those considering that route.

What is an aneuploid embryo?

Aneuploidy is a leading cause of implantation failure and early miscarriage in IVF, and it becomes more common as egg age increases.

When an egg matures incorrectly due to weakened cohesin, the chromosomes may not separate cleanly. The resulting egg carries an abnormal chromosome count, and any embryo created from it will carry that same error. Most aneuploid embryos either fail to implant or are lost in early pregnancy. A small number result in live births with chromosomal conditions such as Down's syndrome, which arises from an extra copy of chromosome 21.

This is not a failure of the IVF process. It reflects the biology of the eggs available at the time of treatment, and it is why success rates in IVF vary so significantly by age.

What about PGT-A testing?

Preimplantation genetic testing for aneuploidy (PGT-A) is a technique used in some IVF cycles to screen embryos for chromosomal abnormalities before transfer. It can help identify euploid (chromosomally normal) embryos, and what an embryologist looks for in an embryo goes far beyond what is visible under the microscope. PGT-A is not suitable for everyone and is a decision to make with your clinical team.

The chromosome glue: what is cohesin?

Cohesin is a protein complex that acts like molecular glue inside an egg, holding together the duplicated copies of each chromosome during the long dormant period before ovulation. Without it, chromosomes cannot be held in the correct position when the egg finally matures and divides.

What makes cohesin so biologically unusual is that it cannot be replaced. In most cells, proteins are regularly broken down and rebuilt. In eggs, the cohesin laid down during foetal development is the only supply available for the entire reproductive lifespan. There is no mechanism to top it up.

This is why the biology of egg ageing is fundamentally different from other forms of cellular ageing. The eggs of a 42 year old are not simply older cells. They are cells that have been holding a finite, irreplaceable molecular structure in place for four decades, and the gradual weakening of that structure is what drives the rise in chromosomal errors.

A review published in Reproductive Medicine and Biology describes how cohesin on egg chromosomes decreases with age, and cohesin loss is now considered one of the central mechanisms of reproductive ageing. Until the new Chiba University study, it was unclear whether eggs had any active mechanism to protect cohesin from breaking down, or whether it simply degraded passively over time.

The new research: what scientists found

The study led by Professor Kei-ichiro Ishiguro at Chiba University's Graduate School of Medicine set out to answer a specific question: do eggs have an active protective mechanism for cohesin, or does it simply degrade over time with no defence?

The answer turned out to be the former, and it centred on a previously unknown protein.

Discovering OMC1

Using single-cell RNA sequencing, the research team compared gene activity in immature foetal eggs with that of male germ cells, which do not undergo the same prolonged dormant period. This comparison led them to identify a previously uncharacterised gene active specifically in eggs shortly before they enter the dormant stage. They named the gene Omc1 and its protein OMC1, short for Oocyte-specific Meiotic Chromosome protein 1.

Crucially, OMC1 was found to sit on chromosomes in the same locations as REC8 cohesin, and to remain there from foetal development through to adulthood.

What happened in mice without OMC1

To understand the protein's function, the team engineered mice that lacked the Omc1 gene. In these mice, REC8 cohesin began disappearing from chromosomes earlier than normal once eggs entered their dormant period. Even young eggs from these mice showed weakened chromosome cohesion and the kinds of chromosome separation errors typically seen in aged eggs.

When the researchers then restored OMC1 in adult mouse eggs, REC8 levels partly recovered and chromosome errors decreased. As Professor Ishiguro noted in the Chiba University press release:

"OMC1 should be regarded not as a factor that stops aging itself, but as a maintenance factor that extends the chromosomal lifespan of eggs."

The human connection

The human counterpart to the mouse Omc1 gene is CCDC201. Previous genetic studies have already linked variants in CCDC201 to early menopause and loss of ovarian function. When the Chiba team tested a truncated version of the mouse OMC1 protein corresponding to one of these human variants, it failed to localise to egg chromosomes and could not restore chromosome cohesion.

This suggests that natural variation in CCDC201 function may partly explain why some women experience earlier reproductive ageing than others.

It is important to be clear: this is early stage research conducted in mice. The findings have not been tested in human eggs, and no treatment or intervention based on this research is available to patients.

What it could mean for IVF in future

The significance of this research lies not in what it changes today, but in the direction it opens up. For the first time, scientists have identified a specific protein that actively maintains the chromosome cohesion machinery in eggs, and have shown that restoring it can partly recover cohesion in adult mouse eggs.

The Chiba University press release notes that within the next decade, scientists may be able to find safe ways to preserve or supplement OMC1 function before cohesin is irreversibly lost. One application researchers have discussed is treating eggs collected during IVF in the laboratory to slow further deterioration of cohesin, potentially improving the proportion of chromosomally normal eggs available for fertilisation.

Professor Ishiguro added that "in the longer term, these findings may contribute to the development of approaches for understanding, assessing, or potentially mitigating the age-related decline in egg quality."

What this does not mean: OMC1 is not a cure for reproductive ageing. The researchers are explicit that it is a maintenance factor, not a reversal mechanism. Cohesin that has already been lost cannot be restored. The research opens a window for early intervention, not a reset.

No treatment based on this research exists today. Any future application would require extensive testing in human eggs and clinical trials before it could be offered to patients. The assisted reproduction field has noted the findings with interest, but the path from mouse study to clinical practice is long.

IVF success rates by age

The impact of egg quality on IVF outcomes is clearly visible in the data published by the Human Fertilisation and Embryology Authority (HFEA), the UK's independent regulator of fertility treatment. Its Fertility Treatment 2024: Trends and Figures report, published in June 2026, shows how birth rates per embryo transferred using a patient's own eggs vary by age.

• Aged 18 to 34: 38% birth rate per embryo transferred, the highest of any age group.
• Aged 43 to 44: 8% birth rate per embryo transferred, the lowest.
• All ages: 30% on average in 2024, up from 20% in 2014.

The rise in the average reflects genuine improvements in laboratory techniques and clinical practice over the past decade. But the age gradient remains steep: a patient in their early 30s is nearly five times more likely to have a birth per embryo transferred than a patient aged 43 to 44. The HFEA notes that its 2024 birth figures are preliminary and may change once validated.

This is not a reason for despair. Around 53,000 patients had IVF in the UK in 2024, and over 21,000 babies were born as a result. People in their 40s do have successful IVF cycles. Understanding how age affects IVF helps set realistic expectations and informs decisions about timing, the number of cycles, and whether options such as egg donation are worth discussing with a clinic.

For a detailed guide to the considerations specific to older patients, see our article on IVF after 40.

How to support egg quality for IVF now

No single thing can guarantee an outcome in IVF. The chromosomal makeup of an egg is set, and the new research reinforces that this is a biological reality, not a failure of preparation. What nutrition and lifestyle can do is support the environment in which eggs grow and mature during the approximately 90 days before egg collection.

This matters because eggs do not simply wait passively during that 90 day window. They are completing a complex maturation process that requires energy, antioxidant protection, and the right nutritional foundations. The conditions during this period may influence the quality of what is retrieved.

Antioxidants and oxidative stress

Oxidative stress, an imbalance between free radicals and the body's ability to neutralise them, is one of the most studied contributors to declining egg quality. A 2025 review in Reproductive BioMedicine Online highlights minimising damage from reactive oxygen species as one of the ways eggs maintain their quality over such long periods. A diet rich in antioxidants, including vitamins C and E, selenium, and zinc, may help support the protective environment around developing eggs.

CoQ10 and mitochondrial support

CoQ10 is one of the most widely studied nutrients in relation to egg quality. It plays a central role in mitochondrial energy production, and mitochondrial health is closely tied to the energy demands of egg maturation. Levels of CoQ10 in the body decline naturally with age, which is one reason it is particularly relevant for women over 35 preparing for IVF.

The research on CoQ10 in IVF preparation includes randomised controlled trials looking at ovarian response and embryo quality, and it is one of the nutrients we recommend most often for women preparing for treatment. No supplement can guarantee IVF success, but CoQ10 may support the energy production eggs rely on as they mature. For guidance on how much to take, including before IVF and over 40, see our guide to how much CoQ10 to take when trying to conceive.

Nutrition and lifestyle

The foundations of egg health are not complicated, but they require consistency across the full three month window before treatment. Key areas include:

• Diet: A Mediterranean-style diet, rich in vegetables, legumes, wholegrains, oily fish, and olive oil, has been associated with better IVF outcomes in observational research. For detailed guidance, see our guides on eating for healthy eggs and what to eat during IVF.
• Alcohol and smoking: Both are associated with reduced ovarian reserve and poorer egg quality. Stopping or significantly reducing alcohol and stopping smoking entirely are among the most impactful steps before treatment.
• Weight: Both underweight and overweight can affect ovarian response and IVF outcomes. Your clinical team can advise on what is appropriate for your individual situation.
• Stress: Chronic stress affects hormone balance. Approaches such as mindfulness, acupuncture, and adequate sleep are worth considering as part of preparation.

The research is promising, but the practical steps available right now are the ones that have always mattered: building the best possible nutritional environment in the months before treatment. Our guide to preparing for IVF covers the evidence in detail and includes guidance on supplements. If you want to start with the fundamentals, our guides to how to improve egg quality naturally and 10 ways to improve egg health are the best places to begin.

Sperm matters too: embryo quality takes two

Much of the conversation about egg quality and age focuses on the woman, and that is understandable given the biology. But embryo quality is a product of both the egg and the sperm, and the male partner's contribution deserves equal attention in IVF preparation.

Sperm DNA fragmentation, oxidative damage to the genetic material inside sperm cells, has been associated with reduced fertilisation rates, poorer embryo development, and higher rates of miscarriage, even when sperm appear normal in a standard semen analysis. Sperm take roughly 74 days to develop, so the nutritional environment today shapes the sperm available at the point of retrieval. Starting preparation three months before a cycle is just as important for men as it is for women.

Key areas for sperm health preparation include antioxidant support to reduce oxidative stress on developing sperm cells, CoQ10 for mitochondrial energy, omega-3 fatty acids for sperm membrane structure, and the micronutrients zinc and selenium. Selenium contributes to normal spermatogenesis, and zinc contributes to normal fertility and reproduction. For men over 40, our guide to male fertility after 40 covers what to focus on and when to start, and is the best next read for any male partner preparing for a cycle.

Over 40 and planning IVF?

If you are in your 40s and considering IVF, the most useful thing you can do right now is start preparing early. The three months before egg collection are the most nutritionally significant window, and the biology does not wait for the perfect moment to begin.

The new research from Chiba University is a reminder that the science of reproductive ageing is moving forward. Researchers are actively working to understand the mechanisms behind egg quality decline, and the field is closer than it has ever been to developing targeted interventions. That progress takes time. In the meantime, the steps you can take today, building the best possible nutritional environment for the eggs you have, remain the most practical path forward.

For those thinking about getting pregnant over 40, or weighing up your options for egg freezing before treatment, our guides to IVF after 40 and preparing for IVF are the practical next step. If you would like personalised guidance on which supplements are most relevant for your situation, book a free 1:1 product consultation with the Zita West nutrition team, and speak to your fertility clinic about your individual treatment plan.

Frequently asked questions

Does egg quality decline with age?

Yes. Egg quality declines progressively from the mid-30s, primarily because the protein that holds chromosomes together inside eggs, called cohesin, weakens over time and cannot be replaced. This increases the proportion of eggs with chromosomal errors, which is the main reason IVF success rates fall with age. According to HFEA data, birth rates per embryo transferred drop from 38% for patients aged 18 to 34 to 8% for patients aged 43 to 44.

Can you improve egg quality after 40?

The chromosomal makeup of eggs is fixed and cannot be changed by supplements or lifestyle. What can be influenced is the environment in which eggs mature during the 90 days before egg collection. Antioxidant support, CoQ10 for mitochondrial energy, a nutrient-rich diet, and stopping smoking may all support the conditions around developing eggs. No intervention can guarantee egg quality, but nutritional preparation is a meaningful step.

What are the signs of poor egg quality?

Egg quality cannot be assessed directly without laboratory testing. In an IVF context, signs that may indicate egg quality issues include a low proportion of eggs fertilising normally, embryos that stop developing early, repeated implantation failure, or a high proportion of aneuploid embryos on PGT-A testing. These are clinical observations, not symptoms you would notice yourself. If you have concerns, speak with your fertility clinic.

What is an aneuploid embryo?

An aneuploid embryo has the wrong number of chromosomes. Most aneuploid embryos fail to implant or result in early miscarriage. Aneuploidy is a leading cause of unsuccessful IVF cycles and becomes more common as egg age increases. PGT-A testing can identify chromosomally normal embryos before transfer, though it is not appropriate for every patient or every cycle.

Does IVF help with poor egg quality?

IVF does not improve egg quality, but it does allow clinicians to retrieve multiple eggs in a single cycle, increasing the chances that at least some will be chromosomally normal. Where egg quality is significantly reduced, egg donation using eggs from a younger donor is an option many clinics discuss with older patients. Your clinical team is best placed to advise on what is appropriate for your individual situation.

Is the egg "glue" treatment available yet?

No. The research identifying OMC1 as a maintenance protein for chromosome cohesion was published in October 2026 and is at an early stage. The study was conducted in mice, not humans, and no treatment or intervention based on these findings is available to patients today. Researchers have suggested that practical applications may be possible within the next decade, but this would require extensive further research and clinical trials.

References

1. Iisaka S, Yoshida S, Shimada R, et al. Oocyte-specific OMC1 is required for maintaining chromosome cohesion through reproductive life. Nature Aging. 2026. https://doi.org/10.1038/s43587-026-01245-5
2. Chiba University. Understanding How Eggs Keep Their Chromosomes Intact Over Decades. Press release, October 2026. https://www.cn.chiba-u.jp/en/news/press-release_e261030/
3. Burgess K. Egg 'glue' could boost IVF success for older women. The Times. 29 October 2026. https://www.thetimes.com/uk/science/article/fertility-ivf-research-women-50z55dmq8
4. Human Fertilisation and Embryology Authority. Fertility Treatment 2024: Trends and Figures. June 2026. https://www.hfea.gov.uk/about-us/publications/research-and-data/fertility-treatment-2024-trends-and-figures/
5. Is age-related increase of chromosome segregation errors in mammalian oocytes caused by cohesin deterioration? Reproductive Medicine and Biology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6955592/
6. Anderson RA, Marston AL, Telfer EE. Oocyte development: it's all about quality. Reproductive BioMedicine Online. 2025;50(4):104804. https://pmc.ncbi.nlm.nih.gov/articles/PMC7617848

Related guides

• Egg Quality After 35: Nutrition, Lifestyle and Supplements
• CoQ10 and Fertility: What the Research Says About Egg Quality, Sperm Health and IVF
• IVF After 40
• Age and IVF: Understanding the Link
• Preparing for IVF: Nutrition, Lifestyle, and Supplements

Egg quality and age are closely linked, and this new research helps explain why. The science may offer new options in future, but the months before treatment remain the window you can make the most of today, for both partners.

Medical disclaimer: this article is for general information and does not replace personal advice from a GP, midwife, fertility clinic or qualified healthcare practitioner, especially if you are pregnant, breastfeeding, taking medication or undergoing fertility treatment.