Age and Fertility: How Age Affects Egg Quality, Quantity, and Your Chances
Key takeaways
- Age is the single strongest factor in natural and assisted conception: both egg quantity and egg quality fall over time, and quality is the part you cannot improve.
- Fertility declines gradually from the early 30s and more sharply from the late 30s, with a steeper fall again in the early 40s.
- Ovarian reserve tests (AMH and antral follicle count) estimate how many eggs are left, but they do not measure egg quality and do not reliably predict your chance of a natural pregnancy.
- Age affects IVF too: success per cycle is highest under about 35 and declines with age, which is why timing matters.
- If you are concerned about your age and fertility, do not wait and see; ask your GP or a fertility specialist sooner rather than later.
Age is the single strongest influence on fertility: as you get older both the number of eggs you have and their quality fall, and quality is the part no treatment can restore. That is the hard truth I wish someone had said to me plainly at 33 rather than at 36. This guide sets out how age affects your chances, what the tests can and cannot tell you, and what the data actually shows.
How age affects egg quantity and quality
Age reduces both how many eggs you have and how good they are, and these are two separate things. You are born with all the eggs you will ever have (around one to two million at birth), and that number falls steadily throughout life, with no new eggs ever made. By the late 30s the pool is much smaller than it was a decade earlier.
Quality matters even more. As eggs age, a greater proportion carry chromosomal errors, which makes them less likely to fertilise, less likely to develop into a healthy embryo, and more likely to end in miscarriage. This is why miscarriage rates climb with age. Crucially, egg quantity can sometimes be worked around in treatment, but the age-related fall in quality cannot be reversed by any drug, supplement, or lifestyle change.
When fertility declines, and how sharply
Fertility declines gradually from the early 30s, more noticeably from the late 30s (around 37), and more steeply again in the early 40s. NICE notes that the chance of conceiving falls with age, and the NHS describes fertility as starting to decline in a woman’s early 30s, with the fall becoming more rapid after the mid to late 30s.
To put a shape on it: with regular unprotected sex, a large share of couples conceive within a year, but that proportion is lower at 35 than at 25 and lower again at 40. The trend is a population average, not a personal forecast: some people in their early 40s conceive without help, and some in their early 30s struggle. What the average tells you is the direction of travel, and the direction is one way.
For me the figures were abstract until they were not. Three years of trying through my mid-30s, then three rounds of IVF, taught me that “we have time” is the most expensive sentence in fertility. I am not saying that to frighten you; I am saying it because earlier information would have changed my choices.
What ovarian reserve testing can and cannot tell you
Ovarian reserve tests estimate how many eggs you have left, but they do not measure egg quality and do not reliably predict a natural pregnancy. The two main tests are AMH (anti-Mullerian hormone, a blood test) and the antral follicle count (an ultrasound scan that counts the small follicles in your ovaries). Together they give a useful picture of how your ovaries might respond to IVF stimulation.
Their limits matter as much as their uses. A reassuring AMH does not mean your eggs are high quality, and it does not mean you will conceive easily; a low AMH does not mean you cannot conceive naturally. Because age drives egg quality, your age remains the better guide to your overall chances than any single reserve number. Treat these tests as one input within a fuller assessment, which is covered in fertility tests and investigations, rather than a verdict.
How age affects IVF and your options
Age is also the strongest predictor of IVF success, because IVF uses your own eggs and so carries the same egg-quality decline. The chance of a live birth per cycle is highest in women under about 35 and declines steadily with age, more sharply from the late 30s. It also helps to think cumulatively across cycles rather than judging by a single attempt; we set out how to read these figures, and the difference between per cycle and per transfer, in IVF success rates.
If you are not ready to try for a baby yet but are concerned about age, freezing eggs while their quality is higher is one way to keep options open; egg freezing explains what it involves and its limits. And if you are already trying and worried about time, do not wait and see: the guidance on when to see a doctor about fertility sets out when to seek help sooner, particularly over 35.
This guide is general information and support, not a diagnosis or individual medical advice. Because fertility can be time-sensitive, please speak to your GP or a fertility specialist about your own situation, sooner rather than later.
References
- Fertility: assessment and treatment for people with fertility problems (CG156), National Institute for Health and Care Excellence (NICE).
- Getting pregnant: how age affects fertility, NHS.
- Age and Fertility, American Society for Reproductive Medicine (ReproductiveFacts.org).
- Ovarian reserve testing, Human Fertilisation and Embryology Authority (HFEA).
Frequently asked questions
At what age does female fertility start to decline?
Female fertility declines gradually from the early 30s, with a more noticeable drop from the late 30s (around 37) and a sharper fall in the early 40s. The decline is driven by both a falling number of eggs and a fall in egg quality. There is wide individual variation, so these are population trends rather than a personal forecast.
Does a good AMH level mean I am fertile?
Not on its own. AMH (anti-Mullerian hormone) and antral follicle count estimate how many eggs you have left (your ovarian reserve), not the quality of those eggs, and they do not reliably predict your chance of conceiving naturally. A reassuring AMH at 42 still carries the egg-quality decline that comes with age. Use the results alongside a full assessment, not in isolation.
Why does egg quality matter more than egg quantity?
Egg quality refers to how likely an egg is to fertilise, develop into a healthy embryo, and result in a live birth. As eggs age, more of them carry chromosomal errors, which is why miscarriage rates rise with age. You can have eggs available but a lower chance that any given one leads to a healthy pregnancy. Quantity falls with age too, but quality is the part that cannot be improved.
Does age affect IVF success?
Yes. Age is the strongest predictor of IVF success: the chance of a live birth per cycle is highest in women under about 35 and declines steadily with age, more sharply from the late 30s. This is because IVF uses your own eggs, so it does not undo the underlying egg-quality decline. See our guide to IVF success rates for how the figures are framed.
Does male age affect fertility?
Yes, though less sharply than female age. Sperm quality gradually declines with age, and increasing paternal age is linked with longer time to conceive and a modestly higher risk of some conditions. Female age remains the dominant factor in a couple's chance of conceiving, but male age is not nothing.
Can I do anything to slow the decline in my fertility?
You cannot reverse the age-related fall in egg quality; no supplement or lifestyle change does that. You can support your overall fertility by not smoking, keeping to a healthy weight, and addressing any treatable conditions early. If you want to preserve your options, egg freezing at a younger age stores eggs while their quality is higher. The most useful step is not to delay seeking advice.
Written by Emma Lawson. Medically reviewed by Dr Priya Nair, MBBS, MRCOG.
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