The headline figure: one in six
In April 2023 the World Health Organization published its first global estimate in more than a decade: about 17.5% of the adult population, roughly one person in six, experiences infertility during their lifetime (WHO, 4 April 2023). The estimate pools studies from around the world. Lifetime prevalence was 17.8% in high-income countries and 16.5% in low- and middle-income countries, a gap much smaller than many people expect.
The WHO stressed the second point as much as the first: infertility is not a problem of rich countries. The difference is in access to care, not in how often it happens.
What "infertility" means in these statistics
The WHO definition is precise. Infertility is a disease of the male or female reproductive system "defined by the failure to achieve a pregnancy after 12 months or more of regular unprotected sexual intercourse" (WHO fact sheet, November 2025). Two consequences follow.
- It is about time, not certainty. Many people who meet the definition at 12 months go on to conceive without treatment. The label describes a delay long enough to justify investigation.
- It can be primary or secondary. Primary infertility means no pregnancy has ever been achieved; secondary infertility means at least one earlier pregnancy. Both are counted.
So "one in six" does not mean that one person in six will never have children. It means that one in six will, at some point, try for a year or more without success.
The odds of conceiving, as the NHS puts them
The NHS gives the figure most couples want first: more than 8 out of 10 couples in which the woman is under 40 will conceive naturally within a year of regular unprotected sex (NHS, Infertility, reviewed August 2023). The same page notes that about one couple in seven has difficulty conceiving, and that after three years or more of trying, the chance of natural conception in the following year falls to one in four or less.
These numbers are averages across many couples. Age, health and the length of time already spent trying all move an individual couple's odds up or down.
Causes: shared between partners
The WHO lists causes on both sides. In men they include blocked reproductive tracts, hormonal disorders, testicular problems that reduce sperm production, and abnormal sperm shape or movement. In women they include tubal disorders (often after untreated sexually transmitted infections), uterine conditions such as endometriosis or fibroids, ovarian disorders such as polycystic ovary syndrome, and hormonal disorders (WHO).
The NHS lists the most common identifiable causes as lack of regular ovulation, poor-quality semen, blocked or damaged fallopian tubes and endometriosis, and adds an important detail: in about a quarter of cases no cause is found. That is often called unexplained infertility. It does not mean nothing can be done; it means the standard tests did not point to a specific problem.
Our explainers on endometriosis, polycystic ovary syndrome and sperm counts go into three of these causes in more detail.
Risk factors that can be changed
Some factors cannot be changed, age first among them. Others can. The NHS lists weight (a BMI of 30 or more, or being severely underweight), sexually transmitted infections including chlamydia, smoking (including passive smoking), alcohol, some environmental exposures such as certain pesticides, solvents and metals, and stress. The WHO adds that many causes of infertility are preventable, which is why it treats prevention, including the treatment of sexually transmitted infections, as part of fertility care.
When to ask for advice
The NHS advice is to see a GP after one year of trying without success, and sooner for women aged 36 and over, or for anyone who already knows of a possible fertility problem. A GP can start basic tests for both partners. Infertility is usually only diagnosed and treated after two years of trying, but tests can begin earlier.
This article explains published figures. It is not medical advice: if you are worried about your fertility, talk to a GP or a fertility specialist, who can look at your own situation.
Access: the other half of the story
The WHO's 2023 report ended on access. Fertility care, the organisation notes, is rarely included in national health coverage, and is largely unavailable or unaffordable in many low- and middle-income countries, where barriers include a lack of trained staff and equipment and high medicine costs. Even in countries with public funding, eligibility rules matter: in England, for example, NHS funding of IVF depends on age and on local criteria, as our article on IVF success rates explains.
Reading the number correctly
Three points are worth keeping in mind when you see "one in six" in a headline:
- It is a lifetime figure: it counts anyone who has ever experienced a year of trying without success.
- It covers both sexes: infertility is not only a women's health issue.
- It describes a common, often treatable situation, not a permanent outcome for most people affected.
For how researchers report outcomes such as pregnancy and live birth, and why the difference matters, see how to read a fertility study.
What happens at a first appointment
A first consultation about fertility usually starts with questions rather than tests: how long you have been trying, how regular periods are, any previous pregnancies, infections, operations or long-term conditions, and lifestyle factors such as smoking and alcohol. Both partners are normally involved, because problems can come from either side, or both.
The first tests are simple. For women, a blood test can check whether ovulation is happening, and tests for infections such as chlamydia may be offered. For men, a semen analysis measures the number, movement and shape of sperm. Depending on the results, a specialist may then suggest an ultrasound scan or tests to check whether the fallopian tubes are open. None of these tests predicts the future with certainty, but together they point to the most likely causes and to the treatments worth discussing.
The emotional side
Trying to conceive for a long time is stressful, and the stress often falls unevenly between partners. Many people find it hard to talk about, partly because the subject is still surrounded by silence in many communities. Clinics in the UK are required to offer counselling to patients considering licensed fertility treatment, and patient organisations provide support and information. Asking for help early, whether medical or emotional, does not commit anyone to treatment.
Where to go next
For people considering treatment, the next questions are usually about IVF and its alternatives. Our explainer on egg freezing covers one option that many people consider before they start trying, and our short history of IVF, from one birth in 1978 to millions, shows how treatment has changed in four decades.