22 April 2022

How does female fertility change with age?

Menopause concept vector illustration.
Cesar Diaz MEDICAL DIRECTOR IVI
Medical Director
Cesar Diaz-Garcia
MD PhD Assoc Prof
IVI London

 

You may already know that for both men and women, fertility changes with age – but do you understand how? In this article, we delve closer into female fertility specifically and how this changes with age, how age affects the chances of conceiving naturally, and some of the numbers you need to be aware of if you plan to have children in the future.

 

When it comes to fertility, why does age matter?

From a medical perspective, getting pregnant – both naturally and through assisted conception – can be a numbers game. Women are born with a finite number of eggs, which gradually decreases naturally over time until the menopause is reached. The menopause normally coincides with your early 50s – however estimates show that by the age of 40, just 3% of egg reserve remains.

When it comes to the aging process and female fertility, it’s important to understand two key points. The first is that changes to fertility levels are inevitable and a natural part of aging. They can’t be slowed down or prevented, no matter how much you exercise, take vitamins or try holistic therapies. However, some habits, such as smoking, can speed up the decline and put your fertility at unnecessary risk. The second is that each woman’s optimal window of fertility is unique and can vary depending on a wide range of factors. For some, fertility can begin to decline sooner than is commonly believed. Sometimes, as early as their 20s. Many women wait until their mid-30s before trying to conceive as this is when they believe they will start to experience a decline in fertility. And although many conceive without any problems, for some this decline could have begun to decline nearly a decade earlier. If you don’t wish to have a child right now but plan to start a family later in life, it can be beneficial to arrange a fertility assessment to inform your family-planning decisions. Fertility assessments are widely available, both at IVI and many other licensed fertility clinics.

While at the age of 25, your odds of conceiving within three months of trying are high, this doesn’t mean it’s necessarily the right time to have a baby. In the UK, the average age of a first time mum stands at 30.7 years old. This figure has continued to climb gradually since 1974, when the average age was 26.4 years old. There are many factors which we could argue have contributed to this change. However, perhaps the most important thing it tells us is that the right time to have a baby is when you feel you’re ready: whether that’s when you feel emotionally and financially stable, when your career is established, or when you meet the right partner.

In recent years, we’ve seen a trend in the UK showing that the number of women giving birth over the age of 40 to be consistently higher than the number who have a baby before the age of 20. For those over 40, there may be a number of reasons for this jump – the growth in fertility treatments being one such factor. IVF has come on in enormous leaps and bounds in the past few decades. In fact, the latest data shows us that the number of babies born through IVF has tripled since 1991 – and IVF birth rates continues to rise.

 

Does age affect fertility treatment outcomes too?

While the changes to fertility levels are well documented for those women trying to conceive naturally, less is widely known about the impact of age on your chances of successful fertility treatment. For women, age impacts both the quantity and the quality of eggs, which we will explain in more detail shortly. This means if you intend to use your own eggs in a fertility treatment, you may have a reduced chance of success depending on your age when you embark on treatment.

The Human Fertilisation & Embryology Authority (HFEA) is the UK’s regulator of fertility clinics. Each year, every licensed clinic is required to report its clinical activity to the HFEA, including success rates. By accumulating this data, the HFEA can break down the national success rate for IVF across the age ranges as follows:

Maternal age

Live birth rate per embryo transferred

Under 35

32.3%

35-37

27.7%

38-39

19.2%

40-42

11.9%

43-44

3.4%

Over 44

3.1%

Please note that these figures indicate success rates on a national scale. IVI London is proud to report success rates consistently above the UK national average, achieving 47% IVF success rate on average across all ages. You can view our success rates here.

Assisted reproductive technologies have been transformational in giving people the opportunity to start a family at a time that’s right for them. However, just as with natural conception, age is one of the most important considerations to take into account.

If you find your fertility has been compromised by age-related factors, there are other options. At IVI, we offer world-class egg donation programs in the UK and overseas. To take part in these programs, egg donors are carefully screened to ensure eggs are healthy and of a high enough quality to be effective when used in a fertility treatment.

 

Aging and egg quality

Normally, the ovaries release the highest quality eggs during the prime reproductive years – this normally peaks between the age of 24 and 28. Gradually, as women get older, egg quality lowers. From the age of 35 onwards, egg quality starts to decline more significantly. The problem this presents when trying to conceive is that the older an egg is, the more likely it is to develop problems during the cell division process.

If there is a problem during the division process, it can lead to genetic abnormalities in the embryo resulting from the egg, such as aneuploidy. This occurs when fertilised eggs have too many or too few chromosomes. A healthy egg should have 23 chromosomes at the point of fertilisation, which is then matched by the sperm to give a total of 46 chromosomes. Genetic conditions such as Down’s Syndrome are a result of having an abnormal number of chromosomes, such as 45 (a missing chromosome) or 47 (an extra chromosome). Importantly, there is a high chance that an embryo with too many or too few chromosomes will end in miscarriage or fail to result in pregnancy at all. This is why older women have a higher risk of miscarriage and a lower chance of pregnancy.

At IVI, women of advanced maternal age are recommended to consider embryo screening as part of their IVF treatment. This allows our scientists to collect and examine the genetic material of an embryo to establish whether it has the correct number of chromosomes and is safe to transfer. This procedure does not harm the embryo.

 

Ageing and egg quantity

Women are born with all of the eggs they will ever have, each stored in a microscopic ovarian follicle. This is known as the ovarian reserve. The number of eggs is somewhere between 1 – 2 million at the time of being born. This number decreases significantly during the childhood and prepubescent years while the follicles remain dormant. The natural decline continues upon reaching puberty, while eggs begin being released each month during ovulation. For the average woman with no known fertility issues, there are around 25,000 eggs remaining in the ovaries upon turning 37 years of age.

If you are concerned about egg quantity or quality, there are ways to optimise the longevity of your eggs to some extent. It is well established that smoking tobacco can accelerate egg depletion, so quitting smoking sooner rather than later can help boost your chances of both a natural pregnancy and an assisted pregnancy. There are also lifestyle factors which can contribute to eggs being lost at a higher rate, such as stress, an unhealthy diet and the excessive intake of toxins, like those found in alcohol. Many medical professionals recommend taking steps towards a healthier lifestyle when trying to conceive with or without assistance.

 

How do I know if my ovarian reserve is low?

There are no set rules that determine precisely how many eggs each woman has at any given time or age. On the other hand, it is possible to gain a relatively accurate estimate that can inform a woman’s choice about how she wishes to proceed with family-planning. The ovarian reserve is commonly measured with a blood test to quantify the level of anti-Müllerian hormone (AMH). AMH is a hormone secreted by ovarian follicles containing eggs. The higher the measure of this hormone in your bloodstream, the higher your ovarian reserve level. We include this simple test within the IVI Diagnostic Pack, our fertility assessment package.

 

We are here to help

For those concerned about the impact of aging on fertility, it can be reassuring to remember that age is no longer the barrier to having a child it used to be. Likewise, if you have been affected by a medical condition which has impacted your ability to have children, there are still lots of options to help you build a family. We work with every patient on an individual basis to deliver a tailor-made treatment journey, which carefully takes into take into account multiple factors including your age and medical history. Contact us today to find out more about how we can help you.

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