Understanding Why Does Females Fertility Decrease with Age and What You Can Do About It

Why does females fertility decrease with age? If you're over 35 and trying to conceive, you've likely asked yourself this question, perhaps after scrolling through fertility statistics, interpreting test results, or absorbing unsolicited advice. It's overwhelming, confusing, and at times, deeply confronting.

But here’s the truth: numbers don’t tell the whole story. That’s why I’ve written this article: to fill in some blanks and comfort you, knowing that your fertility is about more than statistics.

It’s about your whole body, your lived experiences, and the many ways you can support your reproductive health with clarity and care.

In this article, we’ll explore:

• How much female fertility declines with age and why it’s a gradual, not sudden, process

• What AMH can (and can’t) tell you about your ovarian reserve

• The key biological and lifestyle factors influencing fertility decline, including egg quality and hormonal shifts

• The role of mitochondria, oxidative stress, and chromosomal changes like aneuploidy

• How to recognise your body’s subtle fertility signals as you age

• And, most importantly, the lifestyle choices that can help support egg health and reproductive potential, even as fertility evolves

This piece pairs with my other article, What Women Over 35 Need to Know About How to Improve Egg Quality, which offers evidence-backed ways to support fertility naturally. If that article is the “how,” this is the “why.”

So, let’s get started. 

How Much Does Female Fertility Decrease with Age?

Let’s take a breath together, because I know this question can stir up a lot of emotion.

How much does female fertility decrease with age?

It’s one of the most common and confronting questions I hear in my clinic. While the honest answer is that fertility does decline with age, the good news is that it’s NOT a sudden drop but a gradual and complex process influenced by biology and lifestyle.

So, let’s look at what happens inside the body.

First things first, all women are born with a fixed, finite number of eggs. Unlike most other cells in the body, eggs don’t regenerate, so once they’re gone, they’re gone. I know this reality can feel confronting, but understanding the numbers behind it can help make sense of what’s happening over time.

To give you a better understanding, this is how the natural decline unfolds across the different stages of life:

• At birth: A female baby is born with approximately 1 to 2 million eggs.

• Before puberty: This number drops to around 300,000 to 500,000.

• Across the lifespan: Egg numbers continue to decline throughout life, with the rate accelerating with age.

• No renewal: No new eggs are produced in a woman’s lifetime. Therefore, what you’re born with is all you’ll ever have.

• At menopause: Menopause happens once the remaining egg supply is depleted.

Additionally, it is helpful to understand the broader patterns that come with aging. And while everyone’s fertility journey is different, research can give us a general sense of how age may impact the chances of having a baby naturally:

• Age 35: About 15% of women will conceive and give birth within six months of trying.

• Age 40: That number drops to around 10%.

• Age 42: It’s closer to 8%.

To be clear, these are general statistical trends, not the ultimate truth about you as an individual. I’m including them here because they help illustrate how fertility tends to shift over time, even though every woman’s journey is unique.

If you’ve started to notice changes in your cycle, like shorter phases, irregular spotting, or it simply taking longer to conceive, these shifts are your body’s quiet way of asking for more support and a little extra attention.

Remember, fertility isn’t a number or a chart. It’s a living, shifting relationship between your body and your environment. And while age is one part of that equation, it’s not the whole answer.

So, how do we begin to understand the question so many women ask: why does females fertility decrease with age, and what’s really happening inside our bodies over time?

One place to start is with the markers we can measure. While fertility is nuanced and personal, tools like AMH testing can offer a glimpse into ovarian reserve and help guide your next steps.

What Is AMH? 

AMH or Anti-Müllerian Hormone is produced by the granulosa cells of small follicles in the ovaries, typically measuring up to 8mm. It is classified as a homodimeric glycoprotein and belongs to the Transforming Growth Factor (TGF) family, a group of proteins involved in cellular growth and development.

AMH plays distinct roles in male and female reproductive development. In women, it serves primarily as a marker of ovarian reserve, while in men, it plays a role in the development of male reproductive organs during fetal growth.

How Does It Relate to Fertility?

AMH levels are directly linked to a woman's ovarian reserve, as they reflect the number of small follicles in the ovaries, offering insight into how many eggs may still be available. This makes AMH testing a valuable tool for evaluating fertility potential.

Naturally, AMH levels decline with age, following the steady decrease of the egg over time. However, in certain cases, AMH levels can help diagnose certain ovarian conditions, such as Polycystic Ovarian Syndrome (PCOS). 

AMH is measured through a simple blood test that can be done at any point during the menstrual cycle, as AMH levels tend to remain relatively stable throughout. Depending on the laboratory's measurement system, the results are typically reported in nanograms per millilitre (ng/ml) or picomoles per litre (pmol/L).

What the levels mean can vary depending on individual context, but in general:

• A high AMH level may suggest a higher ovarian reserve, meaning more small follicles are present. This can be a positive sign, especially in terms of responding well to fertility treatments.

• A normal AMH level typically indicates a healthy ovarian reserve and good fertility potential for a woman of her age.

• A low AMH level may indicate a diminished ovarian reserve (DOR), suggesting fewer eggs remain. While this can mean a lower chance of success with certain fertility treatments, it doesn't automatically imply natural conception is off the table.

What Factors Affect Fertility Decrease Over Time?

What factors affect fertility decrease? It’s a question I hear often, and it’s such an important one, especially if you’ve wondered quietly to yourself, why does females fertility decrease with age? 

The truth is, it’s rarely just one thing. Female age-related fertility decline is a gradual process shaped by your biology and lifestyle choices.

At the heart of fertility decline are two key biological changes:

• A reduced egg count – As the egg supply decreases, ovulation becomes less predictable.

• A decline in egg quality – As quality declines, the remaining eggs may not develop or divide as reliably as they once did.

Together, these changes can make natural conception more complex as we get older. This tends to become more noticeable after 35, when the drop in egg numbers speeds up, and the eggs that remain are more likely to carry chromosomal changes like aneuploidy.

And while the research helps us understand how much does female fertility decrease with age, it’s not the full story. The peak fertility age for females varies from woman to woman. Therefore, what matters most is how we support your body, starting today, with care, knowledge, and trust in its capacity to heal and adapt.

What Is Aneuploidy and Why Does It Matter?

Aneuploidy refers to changes in the egg's number or structure of chromosomes. These abnormalities can affect how an embryo develops or implants, sometimes leading to difficulties with conception, early miscarriage, or a higher risk of genetic conditions like Down syndrome.

While that may sound clinical or confronting, it simply reflects how your body responds to the passage of time and life experience. This isn’t about blame; it’s about understanding what’s happening so you can support yourself with clarity and compassion.

I want to acknowledge that these are tender topics. If you’ve experienced any of these challenges, know that you are not alone, and none of it is your fault. Fertility is not something we control; it’s something we respond to. Understanding these changes doesn’t diminish your potential but helps you meet your body with compassion and informed care.

So, Why Do Eggs Decline in the First Place?

As mentioned earlier, your eggs have been with you since you were born, which means the ones you’re using in your late 30s or 40s have been sitting in your ovaries for decades. Over time, they imprint everything your body has lived through—physically, emotionally, and environmentally. 

It’s not only about ageing, but the accumulation of life’s experiences, all of which shape the health and potential of your eggs in different ways. Some of the most common influences that can impact your egg decline include:

• Stress

• Illness or chronic inflammation

• Environmental toxins (BPA, phthalates, and parabens in plastics, cosmetics, and some cleaning products)

• Nutrient deficiencies

• The natural wear and tear of time

These factors don’t just influence how you feel; they shape your eggs’ DNA, energy supply, and ability to grow and divide over time. Again, this isn’t about blame; it’s simply how the body reflects your life.

So, what’s actually going on inside the eggs themselves? To answer that, we need to look at two important pieces of the puzzle: 

• How do your eggs get their energy

• How emotional and physical stress can quietly wear them down over time

The Role of Mitochondria and Oxidative Stress

Inside each egg are mitochondria, tiny but powerful structures often called the egg’s energy centres. These mitochondria fuel the complex processes that drive egg maturation, fertilisation, and early embryo development.

However, as we age, mitochondrial function naturally begins to decline. With less energy available, the egg may struggle to complete these essential steps, even if ovulation is happening as expected.

Alongside this shift is another factor: oxidative stress. This type of cellular damage builds up when your body experiences more strain than it can effectively repair. Because eggs don’t regenerate like most other cells, they’re especially vulnerable to this stress over time.

Stressors, like a poor diet, emotional overload, environmental toxins, or even insufficient sleep, create wear and tear at the cellular level. Over time, this contributes to oxidative stress that can quietly chip away at egg quality, often in subtle ways you might not notice until fertility becomes more challenging.

Why Egg Quality Is a Complex Topic Influenced by Many Factors

Firstly, research on how fertility declines with age provides statistics. However, I have yet to come across research done on a truly large sample group and completed over long periods of time. So, we do have research, but we do not have the ultimate answers. Statistics are statistics, and we are all individuals; the way we age and what our genetics are will differ.

For example, if we compare a 40-year-old woman who smoked and drank alcohol all her life to a non-smoker who was on an organic diet, there will be a significant difference in their egg quality. On the flip side, that same non-smoker might have lived with extreme stress her whole life, which can also have a debilitating impact.

This is exactly why egg quality is so complex; it’s not just about age or lifestyle, but the interplay between everything your body has experienced. And that’s also why blanket statements about fertility often fall short. Therefore, we must look at the full picture to truly support it.

Because so many different factors influence egg quality, it’s also incredibly difficult to measure directly. This leads many women to ask, "Is there any test that can really tell me what’s going on with my eggs?"

There Is No Definitive Test for Egg Quality

In short, to conduct an ultimate test and measure egg quality, you would need to extract and destroy the egg in the process. 

However, as mentioned earlier, AMH is an indirect indicator of ovarian reserve. It can be measured through a simple blood test and reflects the number of small follicles, each containing an immature egg, growing in the ovaries. This estimates a woman’s ovarian reserve, or how many eggs she likely has remaining.

But while AMH can give us a snapshot of your egg quantity, it doesn’t tell the whole story. For that, we must listen to your body and the signs, symptoms, and patterns it shares monthly.

What Your Body Might Be Telling You About Fertility

I often see women come into the clinic feeling confused or discouraged by what they’ve read or heard. We search for signs and test results, hoping for clarity, but the truth is, no scan or blood test can capture the full picture.

However, what we can do is listen closely to how the body communicates over time. Sometimes it’s subtle, sometimes more obvious, but some patterns may reflect how your reproductive system responds to the natural changes that come with age. These aren’t diagnoses, and they don’t mean your fertility journey is over. 

Instead, they’re gentle signals that something in your body may need more attention or support. And while every woman’s experience differs, certain patterns show more often as we age. These are often things that might be easy to dismiss but are worth paying attention to.

To give you a better idea, here are some of the more common changes women over 35 might notice in their bodies:

• Difficulty conceiving, even when ovulation is confirmed

• Shorter or increasingly irregular luteal phases

• Mid-cycle spotting or more unstable cycles

• Early or recurrent miscarriages, including biochemical pregnancies

• Thinner endometrial lining (visible in scan )

Now, I want to emphasise that these changes are NOT a diagnosis. They’re clues and nothing more. So, don’t jump to conclusions because nothing is set in stone at this stage. There’s always space to explore, understand, and respond to what your body might be showing you and what it may need next.

Why Does a Female's Fertility Decrease with Age, And What Can You Do to Support It?

While we cannot change the fact that fertility evolves with age, what we can do is work with the body, not against it. 

Many women come to me asking, why does females fertility decrease with age, and while the biological explanations matter, so does what we choose to do next.

There are powerful and practical ways to support egg health, hormonal balance, and your reproductive potential through intentional lifestyle choices.

Below are the areas I focus on most with my clients. These are the steps I trust, use, and have seen to make a real difference. 

• Improving diet: I advocate for a well-balanced Mediterranean diet and eating with the cycle. Eat foods rich in antioxidants, healthy fats, fibre, and micronutrients like folate, zinc, selenium, and vitamin D. This reduces oxidative stress on egg cells, one of the major contributors to DNA damage and poor embryo development. The best foods include berries, leafy greens, fatty fish, avocados, nuts, and whole grains. And of course, you can use my recipe section for inspiration. 

• Regular exercise: Moderate activity for 30–60 minutes, 3–4 times a week, helps improve blood flow to the reproductive organs and reduces inflammation and insulin resistance, both of which are important for ovarian function.

• Stress reduction: Whether through meditation, therapy, journaling, or simply more rest, reducing chronic stress lowers cortisol levels and supports the delicate hormonal signalling from the brain to the ovary.

• Limiting alcohol and avoiding smoking: Smoking damages ovarian DNA and accelerates follicle loss. Heavy alcohol use can disrupt hormone balance. I recommend stopping smoking completely and keeping alcohol to no more than one drink per day, especially when trying to conceive.

• Minimising environmental toxins: Reduce exposure to endocrine disruptors like BPA, phthalates, and parabens found in plastics, cosmetics, and cleaning products, as they can mimic hormones and interfere with egg maturation.

• Maintaining a healthy weight: Being underweight and overweight are linked to poor egg quality and ovulatory disruption. Supporting your body into a healthy range can improve hormonal balance and egg development.

How These Lifestyle Changes Can Help

These intentional shifts won’t reverse time but can meaningfully support fertility. When practised consistently, these foundational areas can create powerful ripple effects throughout your reproductive system by:

• Reducing oxidative stress, leading to fewer chromosomal abnormalities

• Improving mitochondrial function, the energy source of egg maturation

• Stabilising hormone levels like LH and FSH

• Supporting insulin sensitivity for more balanced ovulation

• Enhancing endometrial health for better implantation outcomes

Remember, small, intentional shifts can make a big difference. The goal isn’t perfection; it’s nourishment, rhythm, and connection. Your body already holds the blueprint for fertility; your job is simply to support it, gently and consistently, as it does what it was designed to do.

Thanks for being here,

Irena x

Related Articles:

• What Women Over 35 Need to Know About How to Improve Egg Quality 

• How To Identify the Best Time to Get Pregnant

• The Importance of Preparing for Pregnancy for Women 35+