When you start researching fertility clinics, success rates are usually one of the first things you look at. That's completely understandable — you want to know whether a clinic is going to give you the best possible chance of having a baby.
But here's something that surprises many patients: two clinics can report vastly different-looking success rates and still be delivering the same quality of care. Why? Because not all success rate figures mean the same thing. The way a number is defined, calculated, and presented makes an enormous difference to how it should be read.
This guide explains exactly how UK IVF and IUI success rates are defined, how the HFEA regulates and reports them, what adjustments matter when comparing clinics, and what questions to ask before you put too much weight on any single figure.
Quick Jump:
- The most important IVF metric: Live Birth Rate Per Egg Collection
- IVF success rates by age: the factor that matters most
- What is PGT-A and why does it affect success rate data?
- How IUI success rates are measured
- Fresh vs. frozen embryo transfers: what the data shows
- Why patient mix makes direct comparison difficult
- What good transparency looks like
- How to use the HFEA's clinic finder
- The bigger picture
Who regulates UK fertility success rates?
In the UK, all licensed fertility clinics are regulated by the Human Fertilisation and Embryology Authority (HFEA). The HFEA is the independent regulator established under the Human Fertilisation and Embryology Act 1990, and it oversees every aspect of fertility treatment from clinic licensing to the collection and publication of treatment outcomes.
Every licensed UK fertility clinic is required to submit outcome data to the HFEA. That data is then independently verified and published, making UK fertility statistics some of the most transparent and tightly governed in the world.
You can explore outcome data for any HFEA-licensed clinic including how it compares to the national average using the HFEA's Choose a Fertility Clinic tool
One important thing to know: there is always a data lag. The most recently published verified data (as of 2026) covers treatment cycles from 2022. That's not a gap in transparency it simply reflects the time it takes to track pregnancies through to live birth and complete the verification process.
The most important IVF metric: Live Birth Rate Per Egg Collection
There are several ways to express an IVF success rate, and understanding the differences between them is crucial.
Live birth rate per embryo transferred
This is perhaps the most commonly quoted figure. It tells you how often a single embryo transfer results in a live birth. It's useful, but it has a significant limitation: it doesn't tell you anything about what happened before the transfer. Cycles that failed to produce a viable embryo are excluded from this calculation entirely.
Live birth rate per egg collection
This is a broader and more meaningful measure. It captures the outcome of a complete stimulated cycle — from the point of egg retrieval through to any fresh or frozen embryo transfers that come from that collection. If a cycle produced no embryos suitable for transfer, that's counted in the denominator.
This metric is considered by many clinics, including Care Fertility, to be one of the most honest ways to represent what a full treatment cycle might lead to. It doesn't just show you the best-case scenario; it reflects the complete picture, including cycles where an embryo wasn't available.
Cumulative live birth rate
This takes a longer view, looking at the total probability of a live birth across multiple embryo transfers from a single egg collection (fresh plus all subsequent frozen transfers). For many patients — particularly those who bank embryos over several cycles — this is the most relevant figure of all.
Why the difference matters
Imagine two clinics both report a 40% success rate. If Clinic A calculates this per embryo transferred, and Clinic B calculates it per egg collection, the figures are not comparable. Clinic A's number excludes any cycle that didn't reach transfer; Clinic B's includes them. In practice, the per-egg-collection figure will almost always be lower — but it's the more complete and honest measure.
Always check which denominator a clinic is using before drawing any conclusions.
IVF success rates by age: the factor that matters most
Patient age is consistently the single most important variable affecting IVF outcomes. This is because egg quality and quantity naturally decline as women get older — something that no clinic, however skilled, can fully overcome.
The HFEA publishes UK national average live birth rates broken down by age. Based on the most recently verified data (treatment year 2022), the overall birth rate per embryo transferred in the UK was 23%. But that national average masks significant variation:
- Under 35: Live birth rates are at their highest. Pregnancy rates per fresh embryo transferred reached around 42% in 2022.
- 35–37: Rates begin to decline but remain relatively strong.
- 38–39: A more pronounced drop in success as egg quality decreases.
- 40–42: Birth rate per embryo transferred sits around 10%, though this has improved from 8% a decade ago as techniques have advanced.
- 43–44: Around 5% per embryo transferred using own eggs.
This is why age-specific data is so important when comparing clinics. A clinic treating predominantly younger patients will naturally report higher overall rates than one that sees a higher proportion of older or more complex cases. Neither clinic is performing better or worse — their patient populations are simply different.
When reviewing a clinic's headline success rate, always check whether age-adjusted or age-stratified figures are available. Aggregated figures without any age context are very difficult to use fairly.
What is PGT-A and why does it affect success rate data?
Pre-implantation genetic testing for aneuploidy (PGT-A) is a technique used during IVF to screen embryos for chromosomal abnormalities before transfer. Rather than selecting embryos based solely on how they look in the laboratory, PGT-A can identify whether an embryo has the correct number of chromosomes.
Chromosomal abnormalities (aneuploidy) are a leading cause of both implantation failure and early miscarriage. As women get older, eggs are more likely to produce aneuploid embryos — which is one reason why IVF success rates decline with age. PGT-A can help identify which embryos are chromosomally normal (euploid) and therefore most likely to implant successfully.
When comparing clinic success rates, it's worth asking whether PGT-A cycles are reported separately from non-PGT-A cycles. Clinics that use PGT-A extensively will typically show higher live birth rates per transfer, not necessarily because the clinic is more skilled, but because only chromosomally normal embryos are transferred. Presenting these cycles separately allows for a fairer comparison.
However, PGT-A is not suitable or beneficial for every patient. It adds cost and carries a small risk that embryos are damaged during the biopsy process. It also means that some cycles, particularly those for older patients, may result in no embryos available for transfer once testing is complete.
In 2022, among patients at Care Fertility who had a successful egg collection and underwent PGT-A:
- 85.2% of patients under 38 had at least one chromosomally normal embryo available for transfer
- 58% of patients aged 38 and over had at least one euploid embryo available
Understanding this data helps explain why some patients who start IVF may not reach the transfer stage and why headline success rates don't always reflect the full story of what happened in a given cycle.
How IUI success rates are measured
Intrauterine insemination (IUI) is a simpler fertility treatment than IVF. It involves placing prepared sperm directly into the uterus around the time of ovulation, removing the need for sperm to travel through the cervix. IUI can be performed either in a natural cycle or alongside ovarian stimulation to produce more than one egg.
IUI success rates are typically measured as:
Live birth rate per IUI cycle started: this is the most transparent measure, as it counts every cycle from the beginning, including those that were cancelled before insemination took place.
Pregnancy rate per insemination: this only counts cycles that reached the point of insemination and can therefore appear higher than the per-cycle-started figure.
National IUI success rates are considerably lower than IVF rates, typically ranging from around 15% per cycle depending on age, diagnosis, and whether stimulation is used. IUI is generally recommended as a first-line option for certain patient groups including mild male factor infertility, unexplained infertility in younger women, or for same-sex female couples and single people using donor sperm.
Because IUI cycles are shorter and less invasive than IVF, the total cost and physical burden per cycle is lower meaning patients can often undergo several attempts before considering whether to move on to IVF.
As with IVF, age is a significant factor in IUI outcomes. Success rates decline notably for patients over 35, and most clinics and guidelines suggest that patients should move to IVF if they have not conceived after three to six IUI cycles.
Fresh vs. frozen embryo transfers: what the data shows
One significant shift in UK fertility practice over the past decade has been the increasing use of frozen embryo transfers (FET). Advances in cryopreservation technology — particularly vitrification, a rapid-freezing technique — have meant that frozen embryos now survive the thawing process at very high rates.
HFEA data shows that live birth rates for frozen transfers are now comparable with, and in some age groups slightly higher than, those for fresh transfers. A key reason is that a frozen transfer cycle allows the uterine lining to be prepared separately from ovarian stimulation, which can create a more receptive environment for implantation.
Some clinics now routinely recommend an elective freeze-all strategy — collecting eggs, creating embryos, and freezing all of them for transfer in subsequent cycles — rather than performing a fresh transfer in the same stimulation cycle. This approach can be particularly beneficial for patients at risk of ovarian hyperstimulation syndrome (OHSS), or those who want to undergo PGT-A testing before any transfer.
When comparing clinic success rates, it's worth asking whether they report fresh and frozen transfer outcomes separately, and what proportion of their transfers are fresh versus frozen. A clinic that performs predominantly fresh transfers may be comparing differently to one that uses a high freeze-all rate.
Why patient mix makes direct comparison difficult
Even with all the right metrics in front of you, comparing clinic success rates fairly is challenging — because clinics treat different patients.
A clinic that specialises in complex cases, older patients, recurrent implantation failure, or patients who have failed treatment elsewhere will typically see lower headline success rates than a clinic treating primarily younger patients with straightforward diagnoses. That lower rate does not mean the specialist clinic is performing poorly. It may in fact be achieving better outcomes than any other clinic for that patient group.
The HFEA acknowledges this directly, noting on its own website that success rate information is of limited value in isolation when comparing clinics and choosing where to seek treatment.
Factors that affect a clinic's aggregate outcomes — and therefore complicate direct comparison — include:
- Average patient age — the most significant driver
- Proportion of own-egg vs. donor-egg cycles (donor-egg cycles have higher success rates)
- Case complexity — whether the clinic accepts patients with repeated failures or difficult diagnoses
- Whether PGT-A is routinely used
- Number of cycles performed — clinics with very small numbers can show more extreme figures (high or low) simply due to statistical variation
This is why the HFEA recommends that patients look beyond success rates alone and consider other factors when choosing where to have treatment: the experience and qualifications of the clinical team, the range of treatments and support available, the transparency of pricing, and the patient care culture of the clinic.
What good transparency looks like
When reviewing a fertility clinic's success rate data, here's what to look for:
HFEA verification — has the data been independently verified and submitted to the HFEA? This is a legal requirement for all licensed UK clinics, and verified data is published on the HFEA's website.
Clear definitions — does the clinic clearly explain which metric they are using (per egg collection, per embryo transferred, per cycle started)?
Age-stratified data — are results broken down by age group so you can find figures relevant to your situation?
PGT-A vs. non-PGT-A reporting — are these presented separately so you understand the difference?
Cumulative rates — does the clinic show what happens over multiple transfers from a single collection, not just single-transfer figures?
Honest context — does the clinic acknowledge the limitations of success rate comparisons and direct you to the HFEA's national data for context?
Clinics that present multiple measures, explain what each means, and point you towards independent national data for comparison are demonstrating exactly the kind of transparency you should expect and deserve.
How to use the HFEA's clinic finder
The HFEA's Choose a Fertility Clinic tool allows you to search for any licensed UK fertility clinic and see:
- Their verified live birth rates per embryo transferred
- How those rates compare to the national average for the same age group
- Information about the treatments they offer
- Inspection reports and regulatory history
It's the most reliable starting point for comparing clinics on a level playing field, because every number you see has been submitted using the same definitions and verified by the same independent body.
Use it to identify clinics with consistently strong outcomes — not just a single good year — and to check whether a clinic's results are higher or lower than average for your specific age group.
The bigger picture
Success rates matter. They're a meaningful signal of clinical quality, laboratory standards, and the experience of the team caring for you. But they are one piece of a much larger picture.
The right clinic for you is one that achieves strong, consistently verified outcomes — and one that treats you as an individual, explains your personal chances honestly, and supports you whether treatment is straightforward or complex.
In the UK, you're fortunate to have access to some of the most tightly regulated and transparent fertility data in the world. Use it wisely, ask the right questions, and don't let a single headline figure be the only thing that guides your decision.
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At Care Fertility, our success rates are independently verified by the HFEA and published in full. Our teams are here to explain what those numbers mean specifically for you — not just in general, but for your age, your diagnosis, and your circumstances.
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