What is fertility — and what is infertility?
Fertility refers to the ability to conceive a child. Conception — the moment when a sperm fertilises an egg, creating an embryo — requires several things to happen in sequence: the ovaries must release a mature egg each month (ovulation — the release of an egg from the ovary, which occurs roughly once per menstrual cycle); sperm of sufficient quality and quantity must reach and fertilise that egg; the fallopian tube (the tube carrying the egg from the ovary to the womb) must be open and unobstructed; and the lining of the womb must be receptive to the resulting embryo.
Infertility is clinically defined as the failure to achieve a clinical pregnancy after 12 months or more of regular, unprotected vaginal intercourse. For women aged 36 or over, clinical assessment is typically offered after 6 months — reflecting the steeper natural decline in fertility with age. Infertility is not the same as an inability to ever conceive; for many couples, investigation reveals a treatable cause, and pregnancy follows treatment.[1]
NICE NG257 (updated March 2026) estimates that infertility affects approximately 1 in 7 heterosexual couples in the UK.[1] It is a common medical condition — not a rare misfortune.
The causes of infertility are distributed across both sexes and often involve both partners. Approximately 30% of cases involve a male factor; ovulatory disorders (conditions in which ovulation is irregular or absent) account for around 25%; tubal damage (scarring or blockage of the fallopian tubes, most often from previous infection or endometriosis) for around 20%; uterine or peritoneal factors for around 10%; and in approximately 25% of cases, no identifiable cause is found in either partner — a diagnosis known as unexplained infertility. In around 40% of cases, contributing factors are found in both partners.[1]
Key Terms
- Infertility —clinically defined as the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected intercourse (approximately 2–3 times per week). In women aged 36 or over, assessment is typically offered after 6 months.
- Subfertility —a term sometimes used to describe reduced fertility — where conception may still be possible naturally but is taking longer or is less likely than average.
- Ovulation —the release of a mature egg from the ovary, which occurs roughly once per menstrual cycle. The egg can be fertilised for a window of approximately 12–24 hours after release.
- Ovarian reserve —the quantity and quality of eggs remaining in the ovaries. Reserve naturally declines with age — this is one of the key reasons female fertility falls over time and cannot be reversed.
- AMH (anti-Müllerian hormone) —a hormone produced by small follicles in the ovary, used as a marker of ovarian reserve. Lower levels may indicate reduced egg quantity. AMH can be measured from a blood test at any point in the cycle.
- Follicle —a small fluid-filled sac in the ovary containing a developing egg. Each month, one (or sometimes more) follicles mature under hormonal influence and release an egg at ovulation.
- Ovulatory disorder —a condition in which ovulation is irregular, infrequent, or absent. Common causes include polycystic ovary syndrome (PCOS), thyroid disorders, hyperprolactinaemia (raised prolactin levels), and premature ovarian insufficiency.
- Tubal damage —scarring or blockage of the fallopian tubes, most commonly caused by previous pelvic infection (particularly chlamydia — a sexually transmitted bacterial infection), previous surgery, or endometriosis.
- Semen analysis —a laboratory test that assesses sperm count (the number of sperm), motility (how well sperm move), and morphology (the shape and structure of sperm). It is the primary investigation for male factor infertility.
- IVF (in vitro fertilisation) —a procedure in which eggs are collected from the ovaries after hormonal stimulation, fertilised with sperm in a laboratory (in vitro means "in glass"), and the resulting embryo transferred back into the womb.
- IUI (intrauterine insemination) —a procedure in which prepared sperm are placed directly into the womb at the time of ovulation. Simpler and less invasive than IVF. Used for mild male factor infertility, unexplained infertility, or when the fallopian tubes are open.
- ICSI (intracytoplasmic sperm injection) —a specialised form of IVF in which a single sperm is selected and injected directly into an egg. Used when sperm count, motility, or morphology is significantly impaired.
- Unexplained infertility —a diagnosis given when thorough investigation of both partners identifies no underlying cause. Accounts for approximately 25% of UK infertility cases.
- Folic acid —a B vitamin recommended for all women trying to conceive, taken at 400 micrograms daily before conception and for the first 12 weeks of pregnancy. Reduces the risk of neural tube defects (conditions affecting the development of the baby's brain and spine) such as spina bifida.
Why does it matter?
Fertility difficulties matter because they affect a substantial proportion of couples, carry a profound emotional weight, and are frequently surrounded by misinformation that delays help-seeking. The experience of trying to conceive without success — month after month — is associated with high levels of anxiety, depression, relationship strain, and a sense of personal failure that clinical evidence simply does not support. Infertility is a medical condition. It is not caused by not trying hard enough, not relaxing enough, or not thinking positively enough.
One of the most important things to understand is the 12-month rule: NICE NG257 recommends that clinical investigation and support be offered to couples who have not conceived after 12 months of regular unprotected intercourse (approximately 2–3 times per week).[1] For women aged 36 or over, this threshold is 6 months — because the age-related decline in female fertility is steep, and earlier investigation is clinically justified. Many couples wait longer than this before seeking help, often because they have been told to "just keep trying" or because they feel they should not yet be concerned.
A further significant issue is the widespread misperception that infertility is primarily a female problem. Male factor infertility accounts for approximately 30% of cases in the UK — as many as ovulatory disorders in women.[1] Investigation must include both partners from the outset. A semen analysis (a laboratory test assessing sperm count, motility, and morphology) is quick and straightforward — and frequently the first test to reveal a cause.
The emotional impact of fertility difficulties is real and should be acknowledged. It is clinically appropriate to discuss the psychological dimension alongside the medical one, and support — including counselling — is a recognised part of fertility care.
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What your doctor might do
When to start investigation
NICE NG257 recommends that clinical investigation and support be offered when a couple has not conceived after 12 months of regular unprotected vaginal intercourse (approximately 2–3 times per week).[1] For women aged 36 or over — or where there is a known reason that fertility may be affected (such as a history of pelvic infection, irregular periods, or previous treatment affecting the reproductive system) — earlier referral, after 6 months, is appropriate. There is no value in waiting the full year if a predisposing factor is already known.
Investigation — both partners, simultaneously
One of the most important principles in NICE NG257 is that both partners should be investigated at the same time.[1] Investigating only the woman and then progressing to the man if she is found to be "normal" wastes time and delays diagnosis.
For the woman, initial investigations typically include:[1]
- Blood tests to confirm ovulation — a progesterone level taken around day 21 of the cycle (in a 28-day cycle) confirms whether ovulation has occurred. Early-cycle hormones (FSH — follicle-stimulating hormone, which drives egg development; LH — luteinising hormone, which triggers ovulation; and oestradiol) assess ovarian function
- AMH (anti-Müllerian hormone) — measured from a blood test at any point in the cycle, AMH gives an indication of ovarian reserve (the quantity of eggs remaining). It does not assess egg quality
- Chlamydia screening — chlamydia (a common sexually transmitted bacterial infection that often causes no symptoms) is a leading cause of tubal damage. Screening is standard before any tubal investigation
- Rubella immunity check — women are checked for rubella (German measles) immunity before fertility treatment, as rubella in early pregnancy can cause serious harm to the baby
- Assessment of the fallopian tubes — a hysterosalpingogram (HSG — an X-ray procedure using dye to check that the tubes are open), or in some cases laparoscopy (keyhole surgery), may be offered to check tubal patency (whether the tubes are open)
- Transvaginal ultrasound — to assess the uterus, ovaries, and antral follicle count (AFC — the number of small follicles visible in the ovaries, which reflects ovarian reserve)
For the man, the primary investigation is semen analysis — a laboratory test that assesses sperm count, motility (movement), and morphology (shape). If the first result is abnormal, a repeat test is offered before conclusions are drawn.[1]
Treatment options
The appropriate treatment depends entirely on the cause identified. NICE NG257 sets out a pathway for each main category.[1]
Ovulatory disorders
Ovulation induction using letrozole (Femara) or clomifene (Clomid) — tablets that stimulate the ovaries to produce and release an egg. Where these are unsuccessful, injectable gonadotrophins (hormones — given by injection — that stimulate the ovaries more directly) or laparoscopic ovarian drilling (keyhole surgery to the ovary surface, most commonly used in PCOS) may be considered.
Tubal damage
Where damage is mild, surgical repair may restore tubal function. Where both tubes are significantly damaged or blocked, IVF — bypassing the tubes entirely — is the recommended route. The decision between surgery and IVF depends on the extent and location of damage, and on age.
Male factor infertility
Treatment is guided by severity. For milder cases, IUI (intrauterine insemination — prepared sperm placed directly into the womb at ovulation) is offered. For more significant impairment, IVF is the standard approach. Where sperm count, motility, or morphology is substantially abnormal, ICSI (intracytoplasmic sperm injection — a single sperm injected directly into an egg in the laboratory) significantly improves fertilisation rates.
Unexplained infertility
Where full investigation finds no cause in either partner, NICE NG257 recommends a period of expectant management — continuing to try naturally, with lifestyle optimisation. If pregnancy has not occurred after a further defined period (based on age and how long the couple has already been trying), IUI is offered. If IUI is unsuccessful, IVF is the next step.
For all causes, NICE NG257 recommends optimising general health before and during fertility treatment.[1] This includes achieving a healthy weight (fertility is lower in those with a BMI below 19 or above 29), stopping smoking, limiting alcohol, and taking folic acid (400 micrograms daily) before conception and for the first 12 weeks of pregnancy.
NHS funding and access
NHS funding for IVF in England varies by local Integrated Care Board (ICB — the NHS body that commissions health services for a local area). NICE NG257 recommends that eligible couples be offered up to three cycles of IVF, but actual provision varies significantly across the country. HFEA data shows that approximately 52% of opposite-sex couples aged 18–39 receive NHS funding for their first IVF treatment — leaving a significant proportion who fund treatment privately.[2]
What the research shows
Three areas generate the most questions — and the most anxiety — about fertility: what age does to female fertility, why male factor is so often overlooked, and what IVF can realistically achieve.
Women are born with all the eggs they will ever have. Ovarian reserve — the number of eggs remaining — declines continuously from birth, but the rate of decline accelerates from the mid-30s onwards and becomes steeper after 40. Egg quality (the proportion of eggs that are chromosomally normal) also declines with age, which is why miscarriage rates rise and implantation rates fall as women get older — even with IVF. This is biology, not circumstance, and cannot be reversed.
NICE NG257 reflects this directly: it recommends earlier clinical assessment (after 6 months rather than 12) for women aged 36 or over, and early specialist referral when there is any known risk factor affecting fertility.[1] Waiting the full 12 months before seeking assessment is appropriate for younger women with no known concerns — but there is nothing to be gained by waiting when age itself is already a relevant factor.
Male factor infertility is present in approximately 30% of infertility cases in the UK — and in around 40% of couples, causes are found in both partners.[1] Despite this, the public narrative around infertility still tends to centre on the woman. Semen analysis — which assesses sperm count, motility, and morphology — is a straightforward, non-invasive test that can be completed within weeks. NICE NG257 is explicit: both partners should be investigated simultaneously from the outset.
Common causes of male factor infertility include low sperm count (oligospermia — fewer than 15 million sperm per millilitre), poor sperm motility (asthenospermia — impaired sperm movement), and abnormal morphology (teratospermia — sperm with abnormal shape). In some cases no sperm are present at all (azoospermia). Causes include varicocele (varicose veins around the testicle), previous infection, hormone disorders, and genetic factors. Where male factor is identified, ICSI within IVF significantly improves outcomes.[1]
1 in 32 babies born in the UK is now conceived through IVF — a figure that reflects both how common fertility difficulties are and how significant a role assisted reproduction now plays.[2] HFEA 2022 data shows that nationally, IVF results in a pregnancy in approximately 31% of fresh embryo transfers. This rises to 42% for patients aged 18–34 and falls to around 16% for those aged 40–42.
These are important numbers to hold onto. IVF is a genuine, evidence-supported option — but it is not a guarantee, and success varies substantially with age. The HFEA publishes clinic-by-clinic data so that patients can make informed comparisons. What the statistics also show is that cumulative success — across multiple cycles — is meaningfully higher than single-cycle figures, particularly for younger patients.[2]
📋 Putting it all together
Infertility affects 1 in 7 couples in the UK. It is common, it is a medical condition, and in many cases it has an identifiable and treatable cause. The first step is seeking investigation at the right time — after 12 months of trying, or 6 months if the woman is 36 or over, or sooner if a predisposing cause is already known. Both partners should be investigated from the start.
Male factor is as common as ovulatory disorders in women — it accounts for approximately 30% of UK infertility cases. A semen analysis is a simple, early investigation that should never be postponed. Investigation is not just for the female partner.
IVF is now a well-established part of fertility care — 1 in 32 UK babies is conceived through it. Success rates are real but not guaranteed: approximately 31% of fresh embryo transfers nationally result in a pregnancy, with significant variation by age. Understanding what IVF can and cannot offer — before starting — is part of making an informed decision.
Fertility difficulties carry enormous emotional weight, and the misinformation surrounding them — relax, try supplements, it's probably her — makes everything harder. Understanding what the clinical pathway actually involves, and when to start it, is the most useful thing this article can offer.
References
- NICE (2026). Fertility problems: assessment and treatment. NICE guideline NG257. Published March 2026. nice.org.uk/guidance/ng257
- Human Fertilisation and Embryology Authority (HFEA) (2022). Fertility treatment 2022: preliminary trends and figures. Key facts and statistics. hfea.gov.uk/about-us/media-centre/key-facts-and-statistics
- NHS (2024). Infertility. nhs.uk/conditions/infertility