Unexplained Infertility: What It Means, What Causes It & What to Do Next
Getting a diagnosis of unexplained infertility is one of the most frustrating experiences in fertility medicine — not because something is wrong that can’t be fixed, but because you’re told nothing is wrong at all.
Author
Tassia O’Callaghan
Reviewed by
Kayleigh Hartigan
13 min read
Spotlight:
- Unexplained infertility affects around 1 in 4 people with fertility challenges, making it one of the most common diagnoses in fertility medicine.
- A normal test result doesn’t mean there’s no cause — standard investigations have limits, and something may still be going on that testing hasn’t picked up.
- Spontaneous conception is possible — pregnancy rates with unexplained infertility are actually higher than in many cases where a cause has been found.
- NICE recommends trying for two years in total before IVF is offered — and that timeline can include up to a year before your investigations began.
- IUI and ovulation-stimulating drugs aren’t recommended for unexplained infertility, as the evidence doesn’t support them in this context.
- NHS-funded IVF is available in principle, but eligibility varies depending on where you live.
What is considered unexplained infertility?
Unexplained infertility (sometimes called idiopathic infertility) is diagnosed when a couple has been unable to conceive after a period of regular, unprotected sex — and all the standard fertility investigations have come back normal. [1]
What does “standard investigations” mean in practice? Your doctor will typically have checked:
- Ovulation: Through blood tests measuring hormone levels
- Fallopian tubes: Confirmed open via HyCoSy, with no blockages
- The uterus: No structural abnormalities found
- Sperm analysis: Count, motility, and shape (morphology) all within normal range
For couples, infertility is generally defined as being unable to get pregnant after 12 months or more of regular unprotected sex. If you’re over 36, most clinicians recommend seeking help after six months rather than waiting the full year. [1]
When all these tests return normal results and you still haven’t conceived, the diagnosis becomes unexplained. It’s not a dead end — it’s the start of a different conversation.
How often is infertility unexplained?
More often than you’d think. In about 25% of cases, infertility is unexplained, with no identified male or female cause. That means if you’re in this situation, you’re far from alone — roughly one in four people navigating fertility challenges will receive this same diagnosis. [1,2]
The main causes of infertility include ovulatory disorders, tubal damage, male factor infertility, and uterine or peritoneal disorders — and in about 40% of cases, disorders are found in both partners. Unexplained infertility sits alongside these as one of the most frequently recorded categories. [3]
It’s worth knowing that the 25% figure can vary depending on how thoroughly investigations are carried out. More detailed testing sometimes reveals subtle issues that standard tests miss — which is one reason it’s worth exploring further if you’re not getting answers.
Fertility Test: What It Is, What It Costs & What It Tells You
Whether you’re trying to conceive or simply want to understand more about your reproductive health, a fertility test can help shed light on what’s happening in your body — and what your next steps might be.
What percentage of people have unexplained infertility?
About 1 in 7 couples struggle to become pregnant. Apply the 25% figure to that, and unexplained infertility affects a significant portion of anyone trying to conceive. It’s one of the most common diagnoses in fertility medicine — and yet it’s still one of the least talked about, partly because “no answer” can feel like there’s nothing to say. But it might not be the full story. [3]
What is the most common cause of unexplained infertility?
If there were a single identifiable common cause, it wouldn’t be called “unexplained.” But that doesn’t mean the medical community is in the dark. Research points to several possible underlying factors that standard testing doesn’t always detect.
- Egg quality issues: Standard tests confirm whether ovulation is happening, but they don’t assess the quality of the eggs being released. Subtle abnormalities in egg development or maturation can affect fertilisation even when ovulation appears normal. [4]
- Sperm function: A standard semen analysis checks count, movement, and shape. But it doesn’t test how well sperm actually penetrate and fertilise an egg. There can be functional issues with sperm that simply don’t show up on routine analysis. [5]
- Implantation difficulties: Even if fertilisation happens, an embryo needs to implant successfully in the uterine lining. Problems with endometrial receptivity — how welcoming the lining is — may prevent this without leaving any obvious trace on standard scans. [6,7,8]
- Luteal phase defects: After ovulation, the body produces progesterone to prepare the uterine lining for an embryo. If progesterone levels are too low, rise too slowly, or aren’t sustained for long enough, implantation can fail. This isn’t always picked up in routine testing. [9,10]
- Subtle endometriosis: Mild endometriosis can affect fertility without causing the symptoms that lead to investigation. Some people are diagnosed with unexplained infertility and later found to have mild endometriosis only visible via laparoscopy. [11]
- Immunological factors: In some cases, the immune system may react to sperm or embryos in a way that prevents conception, though this area of research is still developing. [12]
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Is unexplained infertility genetic?
Genetics is increasingly part of the conversation around unexplained infertility, and it’s a genuinely interesting area of emerging research.
Some known genetic conditions — chromosomal abnormalities, single-gene disorders, and variations in genes that control reproductive function — can affect fertility without necessarily producing symptoms that standard tests pick up.
Research suggests that genetic factors may play a role in a meaningful proportion of unexplained cases. As genetic science advances, it’s possible that some cases currently labelled “unexplained” will eventually find a genetic explanation.
For now, genetic testing isn’t a standard part of the unexplained infertility workup — but if you have a family history of genetic conditions, recurrent miscarriage, or other risk factors, it’s worth discussing with your consultant whether additional genetic investigations might be helpful.
Can you get pregnant with unexplained infertility?
Yes — and this is important. Unexplained infertility doesn’t mean you can’t get pregnant. It means that, so far, no clear barrier to pregnancy has been found.
The rate of spontaneous conception in people with unexplained infertility is actually higher than in those with a defined cause, with some studies reporting spontaneous pregnancy rates of 13–15% in the first year of trying, rising to around 35% over the following two years. [13]
For younger people especially, the picture is encouraging. In younger couples, the rate of natural conception could reach as high as 80% over three years of unprotected sex without any treatment. [13]
Time, age, and how long you’ve been trying all influence your individual outlook — but the key message is that a diagnosis of unexplained infertility isn’t a closed door.
Can unexplained infertility go away?
In many cases, yes. Because there’s no identifiable obstacle to pregnancy, some people with unexplained infertility do conceive naturally — sometimes after months or years of trying, and sometimes after making changes to lifestyle factors.
What can shift the odds in your favour?
- Age: The sooner you seek help and explore your options, the more time is on your side. Fertility declines with age, so waiting isn’t always the right strategy, even if spontaneous conception is possible. [1]
- Lifestyle factors: Smoking is likely to reduce fertility in women, and passive smoking may affect the chance of conceiving. There’s no safe level of alcohol during pregnancy, and excessive alcohol intake is detrimental to semen quality. Maintaining a healthy weight and reducing stress where possible can also support reproductive health. [3]
- Timing: Sexual intercourse every two to three days optimises the chance of pregnancy. [3]
- Duration of trying: The rate of spontaneous pregnancy declines significantly with infertility lasting more than three years, so this is an important factor when weighing up whether to pursue treatment. [13]
If you’ve been trying for two years or more without success, the evidence supports moving to treatment rather than continuing to wait — regardless of your test results.
Find the right clinic for you
Choosing a clinic is one of the biggest decisions you’ll make. We’ll find the best options for you and arrange your pre-treatment tests, empowering you from this point onwards.
What is the first step treatment for unexplained infertility?
The first step is often expectant management — a clinical term for “keep trying, with support and guidance.” Your GP or fertility consultant will usually recommend optimising your lifestyle, tracking your cycle, and timing intercourse for your most fertile window before moving to active treatment.
For people with unexplained infertility, NICE advises trying to conceive for a total of two years before IVF will be considered — and this can include up to one year before fertility investigations began. [3]
It’s also worth knowing what’s not recommended. Oral ovarian stimulation medication like clomiphene citrate, anastrozole, or letrozole should not be given to people with unexplained infertility — these drugs haven’t been shown to help in this context, and NICE guidance is clear on this point. [3]
NICE also advises that IUI (intrauterine insemination) shouldn’t routinely be offered to people with unexplained infertility, as evidence shows it isn’t more effective than timed natural conception in this group. That said, individual circumstances vary — so always have the full conversation with your clinician. [3]
What can be done for unexplained infertility?
Plenty. While the diagnosis can feel frustrating, there are real, evidence-based options available to you.
Further investigations
If you’re not yet at the two-year mark, or want to better understand what’s happening, there are additional tests that go beyond the standard workup. These might include:
- A hysteroscopy (a camera inspection of the inside of the uterus) [14]
- A laparoscopy (to check for subtle endometriosis not visible on scans) [15]
- Advanced sperm function testing
- Endometrial receptivity assessment [8]
- AMH (anti-Müllerian hormone) testing to assess ovarian reserve [16]
Not all of these will be appropriate for everyone — your fertility consultant can guide which are worth pursuing in your specific situation.
Lifestyle and wellbeing
It might feel like a small lever to pull when you’re dealing with something this significant, but the evidence does support lifestyle as a meaningful factor. Stopping smoking, moderating alcohol, maintaining a healthy BMI, and reducing chronic stress can all support reproductive health. None of these are guarantees — but they give your body the best possible environment for conception. [1]
IVF (in vitro fertilisation)
NICE recommends IVF for people with unexplained infertility who have not conceived after two years of regular unprotected sex. IVF is particularly valuable here because it moves conception outside the body, giving clinicians a direct window into what’s happening at the fertilisation and early embryo stage — which may reveal issues that standard testing couldn’t detect. [3]
Emotional support
NICE recommends that referral for counselling should be considered at all stages of investigation and treatment because of the emotional weight that comes with infertility. Unexplained infertility can be especially hard to sit with — there’s no clear villain, no obvious fix, and often a sense that you’ve somehow been left without answers. Seeking support isn’t a sign that you’re not coping. It’s a sign that you know what you need. [3]
Is unexplained infertility covered by the NHS?
NICE guidelines advocate that people with unexplained infertility who have not conceived after two years of regular sexual intercourse should be offered NHS treatment — which can include IVF. For women under 40, this means up to three full cycles of IVF. For women aged 40–42, one full cycle may be offered, subject to meeting specific criteria. [3]
However, access to NHS-funded IVF varies significantly depending on where you live. Local Integrated Care Boards set their own eligibility criteria, and funding isn’t always available even when NICE guidance says it should be. The HFEA has noted a decline in NHS-funded IVF cycles in recent years, with more people than ever now paying for treatment privately. [17]
Finding a clinic for unexplained infertility
Not all clinics are the same, and when you’re dealing with unexplained infertility, finding a clinic that takes your diagnosis seriously — and goes beyond standard testing — can make a real difference.
Some clinics offer more advanced investigations as part of their workup: specialist sperm function tests, detailed endometrial assessments, or more in-depth genetic screening. Others specialise in complex or long-standing cases where standard approaches haven’t worked.
Our Clinic Match tool helps you find a fertility clinic that’s right for your specific situation — whether you’re just starting out or have been through treatment before. You can filter by location, NHS availability, specialisms, and patient experience to find the right fit for you.
Unexplained infertility FAQs
Why is unexplained infertility so common?
Partly because fertility is genuinely complex, and partly because standard testing — while thorough — has limits. Tests confirm whether the major processes are happening (ovulation, open tubes, adequate sperm), but they don’t capture everything that needs to go right for conception to occur. Egg quality, sperm function at a molecular level, and the precise conditions needed for implantation are harder to assess with routine investigations.
Should I push for more tests if I’ve been given an unexplained diagnosis?
It’s absolutely reasonable to ask your consultant what additional investigations might be available. Depending on how long you’ve been trying and your individual history, tests like hysteroscopy, laparoscopy, or more specialist sperm analysis might reveal something that standard tests missed. You’re entitled to advocate for yourself.
Does stress cause unexplained infertility?
Stress alone isn’t considered a clinical cause of infertility, but chronic stress can affect hormone levels and may influence cycle regularity. More importantly, fertility treatment is stressful — and managing your emotional wellbeing throughout the process matters, both for you and potentially for outcomes. Don’t underestimate the value of support, whether that’s counselling, community, or both.
Can lifestyle changes really make a difference to unexplained infertility?
For some people, yes. Smoking, alcohol intake, and BMI are all factors that the evidence links to fertility outcomes — so addressing these where you can is worthwhile. It won’t fix everything, and it’s not a guarantee — but it gives your body the best possible foundation, whether you’re trying naturally or going through treatment. [1]
What if IVF doesn’t work for unexplained infertility?
An unsuccessful IVF cycle is hard — there’s no way around that. But it also gives your clinical team valuable information. If fertilisation didn’t happen, or embryo development was poor, that’s new data that can inform the next steps. Many people go on to have successful cycles after an initial setback, since each cycle provides your clinic with more data, and your consultant can discuss adjusted protocols or additional investigations based on what was observed.
Sources
- NHS. Infertility. Last reviewed 9 August 2023.
- National Collaborating Centre for Women’s and Children’s Health (UK). Fertility: Assessment and Treatment for People with Fertility Problems. London: Royal College of Obstetricians & Gynaecologists; 2013 Feb. PMID: 25340218.
- National Institute for Health and Care Excellence. Fertility problems: assessment and treatment. Published 20 February 2013. Last updated 6 September 2017.
- NHS, The Leeds Teaching Hospitals, NHS Trust. Fertility preservation information for women wanting to keep their childbearing options open. 27 October 2025.
- Wang C, Swerdloff RS. Limitations of semen analysis as a test of male fertility and anticipated needs from newer tests. Fertil Steril. 2014 Dec;102(6):1502-7. doi: 10.1016/j.fertnstert.2014.10.021. Epub 2014 Nov 25. PMID: 25458617; PMCID: PMC4254491.
- Timeva T, Shterev A, Kyurkchiev S. Recurrent implantation failure: the role of the endometrium. J Reprod Infertil. 2014 Oct;15(4):173-83. PMID: 25473625; PMCID: PMC4227974.
- Blanco-Breindel MF, Singh M, Kahn J. Endometrial Receptivity. Updated 2023 Jun 7.
- Human Fertilisation & Embryology Authority. Endometrial receptivity testing. 16 October 2023.
- NHS, York and Scarborough Teaching Hospitals. NHS Foundation Trust. Test Directory / Progesterone.
- NHS Imperial College Healthcare, NHS Trust. Recurrent Miscarriage.
- NHS Manchester University, NHS Foundation Trust. Endometriosis & Subfertility. January 2022.
- Kicińska AM, Maksym RB, Szewczyk G. Immunological Causes of Infertility: Diagnostic Perspectives. Biomolecules. 2025 Dec 25;16(1):39. doi: 10.3390/biom16010039. PMID: 41594580; PMCID: PMC12838779.
- Sadeghi MR. Unexplained infertility, the controversial matter in management of infertile couples. J Reprod Infertil. 2015 Jan-Mar;16(1):1-2. PMID: 25717428; PMCID: PMC4322174.
- NHS. Hysteroscopy. 18 January 2024.
- NHS. Laparoscopy (keyhole surgery). 20 December 2023.
- NHS University Hospitals Plymouth, NHS Trust. Anti–Müllerian Hormone (AMH) Test. May 2024.
- Human Fertilisation & Embryology Authority. Latest fertility data ‘paints promising picture’ but pandemic aftershocks may continue to be felt says UK regulator. 20 June 2023.
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