The Patient's Guide to Embryology

Why do eggs decrease in quality as we age?

As a woman ages, the number of eggs in her ovaries decreases, and the remaining eggs are more likely to have chromosomal abnormalities or other defects that can make them less viable for fertilization and pregnancy.

Find out:

  • Why age is important in IVF
  • How the number of eggs change in the ovaries
  • What happens to egg quality
  • How egg quality is affected by the environment around them
  • How to improve egg quality

Why is age important in IVF?

The demand for IVF has grown significantly in the last few decades and one reason is that people are choosing to delay having babies until later in life. This is less of a problem for men who keep making new sperm every second of every day for their whole lives compared to women who have a very rigid biological clock which begins ticking at puberty and stops at menopause.

Female age is the biggest factor determining the success of IVF because it has such a big impact on the quality of the eggs and hence the quality of the embryos. Women are born with all the eggs they will ever have and many are wasted every month. Not only that, but as the pool of eggs gets smaller, the quality of the eggs decreases rapidly too.

Egg number declines with age

At birth, a female has a finite number of eggs in her ovaries and these eggs are stored in structures called follicles. Almost all of the eggs a woman is born with are wasted – out of the millions of eggs in the ovaries at birth, only around 400 are ovulated over her fertile years. During childhood, the ovaries remain relatively inactive and the number of follicles gradually decreases due to a natural process called atresia, where the follicles die off. At the onset of puberty, the brain starts to release hormones that stimulate the growth and maturation of follicles in the ovaries. Each menstrual cycle, many follicles begin maturing but only one mature follicle releases an egg and the others are wasted. The reason for so much wastage is not fully understood but one theory is that the process of atresia helps to eliminate abnormal or damaged eggs, ensuring that only healthy eggs are available for fertilization.

As women get older the pool of egg-containing follicles reduces which means that the ovaries can only produce a limited number of eggs for IVF. Fewer available eggs usually results in fewer embryos being created which gives fewer chances to get pregnant. It is not uncommon for women over 40 to have only 1 or 2 eggs collected for IVF treatment which reduces the chance of success significantly.

Egg quality declines with age

The longer the eggs wait in the ovary, the more they will deteriorate and this can affect both the egg’s DNA and the cellular components inside the egg which drive its functions. These factors play a huge part in fertilization, embryo development and ongoing pregnancy which is why we know that the success rates of IVF rapidly decline as female age increases. This decline begins in the late 20s and accelerates in the mid-30s, with a sharp decline in fertility after age 35.

There are many factors which contribute to egg quality but there are three major reasons egg quality declines as women get older:

1. DNA problems

The decline in egg quality is largely due to problems with the chromosomes. This is because the eggs wait in the ovary at a delicate stage of growth where the chromosomes are vulnerable to damage. By 40 years old, those eggs which are still waiting to be ovulated have been held in this vulnerable state for decades. When they eventually start to mature, the chromosomes easily break apart leaving the egg with missing or extra chromosomes. The vast majority of chromosome abnormalities result in unhealthy embryos so it becomes very difficult to create a healthy pregnancy. At 35 years old it is thought that around 50% of eggs are abnormal and by 42 years old this increases to around 95%. Unfortunately, this is not something the egg can fix. If it does not have the correct number of chromosomes during fertilisation, the embryo will likely be abnormal further down the line.

2. Older eggs cannot repair problems in the embryo

In the early stages of development, embryos have an amazing ability to repair minor DNA errors which are usually introduced by the sperm. Embryos that are made from older eggs are less able to repair these DNA abnormalities compared to younger eggs. This means that embryos made from older eggs are more likely to be unhealthy and often show signs of being poorer quality such as more fragmentation, slower development, or stopping development before they reach the blastocyst stage.

3. Problems with mitochondria

Mitochondria are the powerhouses of the cell and they are responsible for driving many essential processes during egg maturation and embryo development. As eggs get older the mitochondria become dysfunctional and are not able to generate as much energy as the embryo needs. It also means that there may not be enough energy to correctly organise the chromosomes, contributing to the high number of abnormal embryos created from older eggs. Some clinics have even tried inserting donor mitochondria from younger eggs into the eggs of older patients to try to boost the quality, however this is a controversial technique which comes with many ethical considerations and is not used routinely.

Eggs are vulnerable to their environment

Egg development can be affected by a variety of factors in the environment, including nutrition, exposure to toxins, stress, and hormonal imbalances. Eggs are particularly vulnerable to their environment because they spend so long waiting in the ovaries compared to sperm which is constantly regenerating. This means that some of the last eggs to be ovulated have been exposed to a lifetime worth of environmental stress which compounds slowly over the years.

  1. Toxins and pollutants: Exposure to environmental toxins and pollutants, such as lead, mercury, pesticides, and air pollution have been shown to damage eggs and reduce fertility.
  2. Lifestyle factors: Smoking, excessive alcohol consumption, and a poor diet can all potentially impact egg quality and fertility. For example, smoking has been linked to lower fertility rates, and a diet high in processed foods and sugar may negatively impact egg quality.
  3. Stress: Chronic stress can have negative effects on reproductive health and may reduce the quality of eggs. Research has suggested that stress may disrupt ovulation and menstrual cycles, potentially affecting fertility.
  4. Medical conditions: Certain medical conditions, such as PCOS and endometriosis, can affect egg quality and fertility. Women with these conditions may have fewer viable eggs or may be more likely to experience miscarriage or other complications during pregnancy.

Can I improve my egg quality?

Egg quality is difficult to influence because it is the result of genetics and a lifetime of habits. However, it takes around 6 months for eggs to mature before they are ovulated and there is some evidence to suggest that certain treatments or lifestyle changes during this time may improve egg quality in women undergoing IVF.

  1. Lifestyle modifications: Making changes to your lifestyle can potentially improve egg quality. For example, quitting smoking, reducing alcohol intake, and following a healthy diet may help improve the quality of eggs.
  2. Get the right nutrition: Several key nutrients can help to improve egg quality including:
    • Antioxidants such as vitamin C, selenium and coenzyme Q10 can help to protect eggs from oxidative stress
    • Omega-3 fatty acids are important for the development of the cell membrane surrounding the egg
    • Vitamin D helps to regulate hormones that stimulate follicle development and ovulation
    • Avoiding trans fats and excessive sugar which have been linked to lower egg quality
  3. Ovarian stimulation protocols: The protocol used for ovarian stimulation during an IVF cycle may also impact egg quality. Some studies suggest that using a “mild” or “natural” stimulation protocol, which uses lower doses of ovarian stimulating drugs, may lead to higher quality eggs.
  4. Advanced imaging technologies: Some IVF clinics may use advanced imaging technologies, such as time-lapse imaging or polarized light microscopy, to assess the quality of eggs and embryos more accurately.

Not all of these strategies will work for everyone and some may be more effective than others. Additionally, some of these treatments may not be appropriate for all women, and it is important to discuss any potential treatments or changes with your fertility specialist.

Sign up to our Newsletter

The latest news, FAQs answered and IVF explained.

We will never send you spam and you can unsubscribe at any time.