Fertility, age, and planning for pregnancy

For some people, fertility is something they’ve thought about for years; for others, it’s a question that arises more gradually. Wherever you are, understanding how fertility works and how it can change with age, can make planning for pregnancy feel clearer and less uncertain.

This article explains when it can be helpful to start thinking about fertility, how age influences the chances of pregnancy, what testing can and can’t tell you, and when to seek medical advice.

We’ll explain:

• When should you start thinking about fertility?
• How age affects fertility
• Can you measure future fertility?
• Fertility blood tests
• How long does it take to get pregnant?
• Factors that affect how long pregnancy takes
• Infertility concerns: when to speak to a GP or specialist

When should you start thinking about fertility?
 

In our 20s, thinking about our fertility is probably not uppermost in our minds – we take it for granted that by the time we want children, we'll be able to have them. And for some people this is the case. But for others it’s not so simple, and fertility awareness can be useful much earlier.

You don’t have to stick to a specific timeline with fertility planning, in fact rigid schedules might cause unnecessary stress. But understanding how your reproductive health changes with time, what factors can affect it, and what your options are if circumstances change, may allow for more flexibility later.

 

How does age affect fertility?
 

Whether you’re male or female, age is one of the strongest predictors of fertility outcomes. While many people conceive without difficulty later in life, the likelihood of pregnancy generally decreases with age, and the risk of complications increases.

Female fertility and age

Did you know that women are born with their entire lifetime supply of eggs?

At birth, a girl's ovaries contain approximately two million eggs. By puberty, only about 300,000 remain. Of these, 300–400 eggs will be released during a women’s reproductive years. Your peak reproductive years are between the late teens to the mid-twenties [1]. By age 30, fertility starts to decline – very slowly, at first.

From around age 35 onwards, this drop in fertility becomes more prominent. As age increases, particularly beyond 43 it becomes more unlikely for a woman to fall pregnant, even with fertility treatment [2]. There is a higher risk of pregnancy loss and complications. This is mainly due to the significant decline in egg quality; use of egg donation can help improve success rates.

Menopause marks the end of natural fertility, but fertility usually declines before this point.

How does age affect female fertility?

As women age, the genetic material in their eggs is more likely to accumulate errors or faulty DNA, which reduces the chances of a viable pregnancy. Women in their 20s will have mostly normal eggs, whereas women in their 40s will have mostly abnormal eggs, making it more difficult to conceive.

Changes in egg quality is one of the primary reasons fertility declines with age, but this is not the only reason.

Factors that contribute to age-related declines in fertility: 

• Changes in egg quality - Women in their late 30s or 40s tend to have more eggs with abnormal chromosomes, making it more difficult to conceive and early miscarriage more likely [3].
• Frequency and efficiency of ovulation – Periods become less regular and frequent as a woman approaches menopause. This usually becomes noticeable in the 40s, but it may occur earlier, especially for women who experience early menopause. 
• Medical conditions – Some disorders that affect fertility are more prevalent with increasing age, such as uterine fibroids and endometriosis.
• Increasing risk of pregnancy complications – Pregnancy later in life comes with a higher risk of complications, like pre-eclampsia. For this reason, if you’re 40 or over, you’re more likely to be offered additional monitoring and consultant-led care. 
• Increasing risk of miscarriage — The risk of miscarriage increases with age. For women under 30, about 1 in 10 pregnancies end in miscarriage. This risk doubles for women in their late 30s. For women over 45, more than half of pregnancies end in miscarriage [3]. 

Male fertility and age

Male fertility also changes with age, although usually more gradually.

With increasing age, sperm count, motility, and shape may decline, and sperm DNA fragmentation becomes more common. These changes can reduce the chances of conception and may increase miscarriage risks. While people with testes can remain fertile later into life, age is still a relevant factor in pregnancy outcomes.

The following chart shows how male and female fertility varies with age.

Adapted from British Fertility Society [1].

Can you measure future fertility?
 

Unfortunately, you can’t predict fertility with absolute certainty. But fertility testing can provide useful information about reproductive health and may help identify potential issues early.

Testing can be helpful when:

• You are planning to try for pregnancy in the near future
• Pregnancy has not occurred after a period of trying
• There are known risk factors or medical conditions affecting fertility
• You want baseline information to support longer-term planning

Fertility blood tests: what they measure and when they’re useful

What is a fertility blood test?

A fertility blood test measures levels of specific hormones involved in reproduction. These hormones regulate egg development, ovulation, sperm production, and menstrual cycles.

Blood tests can:

• Provide insight into how your reproductive system is functioning
• Suggest whether your hormone levels are typical for your age
• Help guide further testing or medical assessment

They cannot:

• Confirm whether pregnancy will occur
• Accurately predict how long your fertility will last
• Assess egg or sperm quality directly

Results are most useful when interpreted alongside your age, medical history, symptoms, and (where relevant) other investigations.

Fertility blood tests that may be used

Some tests measure hormones related to egg development and ovulation.

These include:

• Follicle-stimulating hormone (FSH) – Involved in stimulating egg development. Persistently high levels may suggest reduced ovarian response.
• Luteinising hormone (LH) – Triggers ovulation and supports hormone production.
• Oestradiol – A form of oestrogen produced by developing eggs; helps prepare the uterus for implantation.
• Anti-Müllerian hormone (AMH) – Reflects the number of follicles in the ovaries and is often used as a marker of ovarian reserve.

Other tests can measure hormones related to sperm production.

These include:

• Testosterone – Essential for sperm development.
• FSH and LH – Also play roles in sperm production and testicular function.

It can also be useful to measure factors such as levels of B vitamins or vitamin D, minerals like magnesium, and your thyroid function.

When should fertility blood tests be taken?

Some fertility blood tests depend on timing within your menstrual cycle. For example, certain hormone panels are often measured early in the cycle (commonly around day three). Other tests, such as AMH, can usually be taken at any point.

It’s important to get your timing correct, because hormone levels naturally fluctuate. A healthcare professional can advise you on when testing is best.

Fertility blood test limitations

Fertility blood tests can indicate whether your hormone levels fall within expected ranges and whether further investigation may be useful. But normal results don’t guarantee fertility, and abnormal results don’t necessarily mean pregnancy is impossible.

Blood tests are best viewed as one piece of a larger picture rather than a definitive answer.

What other types of fertility tests are there?

Blood tests are often used alongside other investigations.

These include:

• Ultrasound scans to assess ovarian follicles
• Semen analysis to evaluate sperm count and quality
• Imaging to check the uterus or fallopian tubes

Using multiple tests together provides a more complete assessment than any single test alone.

How long does it take to get pregnant?
 

Time to pregnancy varies widely. Some people conceive quickly, while others take longer, even when no fertility problems are identified.

In general:

• Many pregnancies occur within the first year of regular, unprotected sex
• It’s completely normal for conception to take several months
• Time to pregnancy tends to increase with age

Don’t worry if you find your journey doesn’t follow these rules; variation is expected and doesn’t automatically mean there is a problem.

Factors that affect how quickly pregnancy happens
 

We’ve already talked about how age can affect your fertility, but what are some other factors that can make a difference?

Reproductive health

Some of these conditions are treatable or manageable, particularly when identified early.

Conditions that may affect fertility include:

• Polycystic ovary syndrome (PCOS)
• Endometriosis
• Blocked fallopian tubes
• Uterine fibroids
• Premature ovarian insufficiency
• Sperm-related factors
• Presence of sexually transmitted infections (STIs)

General health and lifestyle

You can read more about lifestyle habits that can affect fertility in our blog, but there are some factors which play an important part in your reproductive health.

Factors such as:

• Smoking and recreational drug use can reduce fertility
• Excessive alcohol intake may impair reproductive function
• Very low or very high body weight can disrupt hormone balance
• Certain medications and chronic illnesses may affect fertility

Frequency and timing of sex

Although you might be tempted to aim for timing sex around ovulation, research shows that regular intercourse is actually more beneficial.

This is because:

• Regular intercourse every two to three days maximises the chance of sperm being present during ovulation
• Strictly timing intercourse around ovulation is not necessary for many couples and may increase stress – which is counterproductive to conceiving
• If a woman’s periods are irregular, it can be hard to tell when ovulation is happening

When to speak to a GP or fertility specialist
 

Seeking advice earlier does not mean treatment is inevitable; it often provides reassurance or guidance.

Medical advice is often recommended if:

• Pregnancy has not occurred after one year of trying
• You are over 35 and have been trying for six months
• Periods are irregular or absent
• There is known reproductive or medical history affecting fertility

Fertility testing, including blood tests, can support informed planning but should be interpreted carefully. Results are most helpful when discussed with a healthcare professional who can place them in context and advise on next steps if needed.

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References

1. At what age does fertility begin to decrease?, British Fertility Society. [cited 10 Jun 2026]. 
2. HFEA: UK fertility facts and statistics, 2004, Human Fertilisation & Embryology Authority (HFEA) [Internet]. [cited 11 Jun 2026].
3. Risk of miscarriage linked strongly to mother’s age and pregnancy history 2019, BMJ Group. [cited 11 Jun 2026].
4. NICE. Scenario: Management of infertility. In: CKS [Internet]. 2023 [cited 9 Jun 2026].