Your Age and IVF Success

What actually changes with age?

Women are born with the eggs they will have throughout their reproductive lives. The number of eggs remaining gradually decreases over time, but quantity is only part of the reason fertility changes with age.

There is also a change in the proportion of eggs capable of creating chromosomally normal embryos. As maternal age increases, chromosomal abnormalities in eggs and embryos become more common, which contributes to lower implantation and live birth rates and a higher risk of miscarriage.

These two things are often grouped together when people talk about “egg quality”, but it is helpful to separate them. How many eggs you may have available and the reproductive potential of those eggs are not the same thing.

What does AMH actually tell us?

AMH, or Anti-Müllerian Hormone, has become one of the best-known fertility tests. Patients sometimes arrive at their first appointment knowing their AMH result before almost anything else about their fertility, and it is easy to understand why that number can take on so much importance.

AMH is useful, but it needs to be interpreted correctly. Along with an antral follicle count on ultrasound, it can help us assess ovarian reserve and anticipate how the ovaries may respond to stimulation during IVF. This can be valuable when planning treatment and estimating the number of eggs we may have an opportunity to work with.

The reverse is equally important. A younger woman with a low AMH should not assume that she has poor-quality eggs or no chance of pregnancy. A lower ovarian reserve may mean fewer eggs are available or fewer may be collected during IVF, but that is different from saying those eggs are necessarily of poor quality.

We spend time explaining this because AMH can otherwise become much more powerful psychologically than it deserves to be clinically. A high result can provide false reassurance, while a low result can create enormous anxiety. It is one piece of useful information, not a fertility score.

If my AMH is good, why does my age still matter?

This is a question we hear frequently, particularly from women who have been told they have a good ovarian reserve for their age.

A higher AMH may suggest that more follicles are available and that the ovaries could produce a stronger response to IVF stimulation. That can certainly be helpful because having more eggs to work with may create more opportunities for fertilisation and embryo development. It does not, however, change the age of the eggs themselves.

A 40-year-old woman with a relatively high AMH may respond very well to stimulation and produce a good number of eggs. Her age remains relevant when we consider the likelihood that each of those eggs will ultimately contribute to a chromosomally normal embryo.

A younger woman with a lower AMH presents a different situation. She may produce fewer eggs, but her age may be more favourable when considering the reproductive potential of each egg. Neither patient can be understood properly from one number alone, which is precisely why we look at ovarian reserve and age together rather than treating one as an answer to the other.

Can IVF overcome the effect of age?

IVF can do remarkable things, but it cannot make an egg younger. What IVF allows us to do is stimulate the ovaries so that a number of follicles may develop during a treatment cycle, collect the eggs that are available, fertilise mature eggs and observe embryo development in the laboratory. Where appropriate, genetic testing can provide further information about embryos before transfer.

These are opportunities that do not exist in natural conception, but the underlying biology of the egg remains important. Starting IVF therefore does not remove the effect of reproductive age. IVF allows us to work with the eggs available at that point in time; it cannot reverse the biological changes that have occurred in those eggs over the years.

What do we learn once IVF actually begins?

Before treatment, we work with the information available to us: age, medical and reproductive history, ovarian reserve testing, ultrasound findings, sperm factors where relevant and any previous fertility treatment. Once IVF begins, we start learning things that could not necessarily have been known beforehand.

We see how the ovaries respond to stimulation and how many eggs are collected. We learn how many of those eggs are mature, how fertilisation progresses and how the embryos develop over the following days. If genetic testing is undertaken, additional information may become available.

This does not mean one IVF cycle provides every answer. Human reproduction is far too variable for that. It does mean that the patient's own response to treatment can add information that an age bracket, AMH result or population statistic cannot provide.

This is an important part of the doctor-led model at No.1 Fertility. We are interested not only in whether a cycle resulted in pregnancy, but in what happened during that cycle and whether anything we learned should influence the next clinical decision. Sometimes there is something meaningful to reconsider; sometimes the treatment progressed as expected and there is no clinical reason to change it. The point is to review the treatment rather than assume that age, on its own, explains everything.

Why does age affect the chance of obtaining a chromosomally normal embryo?

An embryo normally contains a particular number of chromosomes. An embryo with the expected chromosome number is described as euploid, while an embryo with an abnormal number is described as aneuploid. Aneuploid embryos become more common as maternal age increases, which is an important part of the relationship between age and fertility because chromosome abnormalities can contribute to failure to implant, miscarriage and some chromosomal conditions.

This is where our own No.1 Fertility data becomes particularly useful, not because we want to present another success-rate percentage, but because it helps explain what age can actually mean during IVF.

Across the age groups represented in our data, pregnancy rates following transfer of a euploid embryo remain relatively consistent. What changes considerably with increasing maternal age is the likelihood of obtaining a euploid embryo in the first place.

That distinction matters. If we looked only at pregnancy rates following embryo transfer, we would miss an important part of the journey. For an older patient, a significant challenge may occur earlier — in creating an embryo with the chromosomal potential to progress to transfer and pregnancy.

This is one reason we publish this information. We want our results to do more than tell patients how No.1 Fertility has performed; where possible, we want the data to help patients understand their own treatment and the biology behind the numbers.

We have deliberately kept the genetics discussion brief here because PGT-A and embryo genetic testing deserve a proper explanation of their own. Patients considering genetic testing can find detailed information about its uses, limitations and the different forms of PGT in our dedicated Genetics section.

Is 35 really the age when fertility suddenly declines?

The age of 35 appears frequently in fertility information, which can give the impression that something dramatic happens on a woman's 35th birthday. Biology is not that precise.

Reproductive ageing is a gradual process. Fertility does not remain unchanged at 34 and suddenly collapse at 35. The reason 35 appears so often is that it has traditionally been a useful clinical and statistical marker as age-related changes become increasingly relevant.

What does change is the value of time as reproductive age advances. For someone already experiencing difficulty conceiving, another year can have different implications at 39 than it might at 29. That does not mean every 39-year-old should immediately start IVF, just as it does not mean every 29-year-old can safely assume there is no reason to investigate a fertility concern.

I'm healthy and fit. Doesn't that count for something?

It certainly does, but perhaps not in the way people sometimes hope when thinking about fertility.

We see women in their late 30s and 40s who exercise regularly, eat well, do not smoke and feel healthier than they did ten years earlier. That is excellent for general health and can be important when preparing for pregnancy, but ovarian ageing follows a different biological timetable.

This can feel counterintuitive because so much else about ageing has changed. People are healthier for longer, careers develop later, relationships may begin later and having children in the late 30s and 40s is much more common than it once was. It is understandable that reproductive life might be expected to have shifted in the same way, but the biology of the egg has not changed simply because the way we live has.

Being healthy remains valuable, and age should never be interpreted as meaning pregnancy cannot occur. The important distinction is that general fitness cannot tell us the chromosomal potential of an egg. We would rather explain that clearly than allow someone who feels exceptionally healthy to assume that age is therefore no longer relevant to fertility.

What if I've already had unsuccessful IVF?

This is where we think an individual fertility story becomes particularly important. Previous treatment gives us something an age-based graph cannot: information about what actually happened to you.

When we review an unsuccessful IVF cycle, we can look at how the ovaries responded, the number of eggs collected, how many were mature, what happened with fertilisation, how the embryos developed and what happened following transfer. If there have been several cycles, looking at them together may reveal patterns that are less obvious when each cycle is considered separately.

Age may still be an important part of the explanation, particularly where the probability of obtaining a chromosomally normal embryo has declined. But we do not think age should become a convenient answer that prevents us from looking carefully at the rest of the treatment history.

Sometimes that review identifies something worth investigating or approaching differently. Sometimes it confirms that the previous treatment was entirely reasonable and that the outcome reflects the uncertainty inherent in IVF. Both conclusions can be valuable if they are reached after properly considering what happened.

When should I ask for fertility advice?

For women under 35 who have been trying to conceive without success, fertility assessment is generally recommended after 12 months. From age 35, assessment is generally recommended after six months, while women over 40 may benefit from seeking advice sooner. There are also reasons to seek advice earlier at any age, including irregular or absent periods, known reproductive conditions, concerns about sperm or a previous fertility history that may affect conception.

So, what does your age actually mean for your chance of success?

Age gives us important information about reproductive probability, particularly when treatment involves your own eggs, but it is one part of a much larger clinical picture. Ovarian reserve, reproductive and medical history, sperm factors where relevant, previous pregnancies and previous fertility treatment all add information. If IVF is undertaken, the way an individual patient responds provides another layer of information that no age-based graph can give us beforehand.

This is why we do not think an age, AMH result or website success-rate percentage should be treated as a verdict on someone's fertility. They are pieces of information that become useful when they are interpreted together by someone who understands the patient's history and what they are trying to achieve.