Success Rate Methodology
How Medical Navigator evaluates and compares fertility clinic success rates. We do not calculate the comparison ourselves - we reproduce what each country's regulator or registry publishes. Because the United Kingdom and Spain use different national systems, each has its own methodology below.
United Kingdom (HFEA)
What this page shows
For each licensed fertility clinic in the United Kingdom, we show a single comparison label - whether the clinic's live birth rate is higher than, similar to, or lower than the UK national average.
We do not calculate this label ourselves. It is the comparison published by the Human Fertilisation and Embryology Authority (HFEA), the UK's fertility regulator, on its Choose a Fertility Clinic service. Every UK clinic is legally required to report every treatment cycle to HFEA, and HFEA publishes the resulting comparison for each clinic. We reproduce that comparison unchanged.
Where available, the clinic's most recent Care Quality Commission (CQC) inspection rating is shown alongside it. Clinics are not ranked (see What we deliberately do not show).
How to read the labels
- Higher than the national average
- HFEA's analysis found the clinic's live birth rate above the UK average by a margin unlikely to be due to chance.
- Similar to the national average
- HFEA's analysis found the clinic in line with the UK average. Most clinics fall here - either they genuinely are typical, or the numbers are not large enough to say otherwise.
- Lower than the national average
- HFEA's analysis found the clinic's live birth rate below the UK average by a margin unlikely to be due to chance.
"Similar" is not a negative judgement. Most clinics fall into this category. It means the clinic performs in line with UK clinics as a whole.
"Lower" needs context. A number of clinics that show as lower are NHS units and large hospital departments that treat older patients, complex cases, and patients other clinics decline. A more difficult caseload lowers success rates even when the medical care is excellent, and HFEA's headline comparison does not adjust for case complexity.
How the comparison is made
The comparison is HFEA's, made against the UK national average - the rate across all treatment cycles in the country. Because that average is weighted by volume, it reflects what happens to a typical patient in the UK, rather than at a typical clinic. (This is the main difference from our Spanish comparison, which uses the average across clinics. The two labels are therefore not directly interchangeable - see the note at the end.)
The measure is live births per embryo transferred, excluding donor eggs and genetically tested embryos. We chose this measure because it is the one HFEA itself headlines, because it is the fairest single measure across clinics with different transfer policies, and because it is the same measure we use for Spain, so the two countries can be read together.
HFEA applies a conservative statistical threshold (99.8% confidence). Only clear, unlikely-to-be-chance differences earn a "higher" or "lower" label; everything else is "similar". Smaller clinics need a larger gap to be flagged, because their results carry more uncertainty.
Important caveats
HFEA publishes more than one measure, and they do not always agree. For each clinic HFEA reports four comparisons - births per embryo transferred, overall IVF birth rate, pregnancies per treatment started, and births per treatment started. We show one of them. In most clinics the four do not all point the same way: a clinic can be above average per embryo transferred and below average per treatment started, for example because it transfers embryos selectively. The label we show is a fair summary but it is not the whole picture; HFEA's own clinic page shows all four.
No adjustment for patient complexity. HFEA's headline comparison compares raw outcomes. Clinics treating younger patients, or declining difficult cases, will tend to show higher rates.
Not every clinic has a label. HFEA does not publish a comparison for every licensed centre - typically because the clinic performs too few cycles for a reliable comparison, because it is a storage or sperm-bank licence rather than a treatment clinic, or because it is a satellite of another centre. Satellite branches operate under their parent centre's licence, and HFEA reports the parent's results, not the branch's. We show no label for satellites rather than borrowing the parent's, because a parent clinic's results say nothing reliable about a branch in another town. A missing label means "not separately reported", not "poor".
Reporting period. HFEA updates its comparison as newly verified data comes in, so a clinic's label can change between updates, especially for smaller clinics. The period each comparison covers is stated on HFEA's own page for that clinic.
Different clinics, different patients. Private clinics and NHS units in the UK often treat systematically different populations. The national average blends both.
What we deliberately do not show
- Bare success rates or a ranking. A single number stripped of its uncertainty invites false precision and misranking. The like-for-like label - not a percentage - is the comparison we stand behind.
- A ranking or "best clinic" badge. Most clinics are statistically indistinguishable from the average, so any ranking would be misleading.
- A parent clinic's results on a satellite branch. See above.
- Cost, location, or patient experience. This comparison is about one clinical outcome only. Patient reviews and CQC inspection ratings are shown separately and are not blended into it.
A note on comparing UK and Spanish labels
Both countries use the same measure (live births per embryo transferred) and the same statistical threshold (99.8%), so the labels are as comparable as two national systems allow. They differ in one important way: the UK label compares each clinic with the national average of all treatments, while the Spanish label compares each clinic with the average clinic. In the UK the comparison is made by the regulator; in Spain it is made by us from the regulator's published ranges. Read each label within its own country.
Source & corrections
Based on the HFEA Choose a Fertility Clinic service, reproduced without alteration. If you represent a clinic and believe the label shown does not match what HFEA publishes for you, please contact us - we can correct a matching error or publish a correction note. We cannot change the underlying comparison; that is published by HFEA directly.
Spain (SEF)
What this page shows
For each fertility clinic in Spain that reported to the Spanish Fertility Society (SEF) in 2024, we show a single comparison label - whether the clinic's live birth rate is higher than, similar to, or lower than most other Spanish fertility clinics.
The label is based on frozen embryo transfers, which make up the large majority of modern IVF cycles. For the very few clinics with no usable frozen data, it is based on fresh transfers instead. Clinics are not ranked; the like-for-like label is the headline (see What we deliberately do not show).
How to read the labels
- Higher than most peers
- The clinic performs better than the typical Spanish clinic by a margin unlikely to be due to chance.
- Similar to most peers
- The clinic performs in line with the typical Spanish clinic. Most clinics fall here - either they genuinely are typical, or the data isn't precise enough to say otherwise.
- Lower than most peers
- The clinic performs below the typical Spanish clinic by a margin unlikely to be due to chance.
"Similar to most peers" is not a negative judgement. Most clinics fall into this category. It means the clinic performs in line with what other Spanish clinics achieve.
"Lower than most peers" needs context. Many clinics that show as lower are large public university hospitals that treat older patients and more complex cases. A higher-difficulty caseload tends to lower success rates even when the medical care is excellent, and we cannot adjust for case complexity because SEF does not publish it.
How the comparison is made
Each clinic is compared against the typical Spanish fertility clinic - the equal-weighted average across all SEF-reporting clinics, so every clinic counts the same regardless of size. This answers the question a patient actually asks: "How does this clinic compare to the others I could choose?"
We use a conservative statistical threshold (99.8% confidence, the same level the UK's HFEA uses on its Choose a Fertility Clinic tool). Only clear, unlikely-to-be-chance differences earn a "higher" or "lower" label; everything else is "similar". Smaller clinics need a larger gap to be flagged, because their results carry more uncertainty.
Important caveats
No adjustment for patient complexity. Clinics that treat younger patients or screen out complex cases tend to show higher rates than clinics treating older or higher-risk patients. SEF data does not let us control for this.
Voluntary reporting. SEF reporting is voluntary. About 325 clinics reported for 2024; 222 had data precise enough to compare. Clinics with weaker outcomes may be under-represented, which nudges the "typical" reference upward.
One label, from one transfer type. SEF reports fresh and frozen transfers separately, and a clinic can be strong on one and weak on the other. We show one label per clinic, taken from its frozen-transfer results because those are the majority of cycles today. About 83 clinics could be compared on only one transfer type - nearly all missing fresh - so for them there was no choice to make.
Single year. Results are from the 2024 reporting year and can vary year to year, especially for smaller clinics.
What we deliberately do not show
- Bare success rates. SEF publishes each clinic's results only as ranges, so any single percentage we quoted would be our reconstruction, not a reported figure. A number stripped of its uncertainty invites false precision and misranking. The like-for-like label - not a percentage - is the comparison we stand behind.
- A ranking or "best clinic" badge. Most clinics are statistically indistinguishable, so any ranking would be misleading.
- Cost, location, or patient experience. This comparison is about one clinical outcome only.
Source & corrections
Based on the SEF clinic registry, 2024 reporting year. If you represent a clinic and believe the comparison shown is incorrect, please contact us - we can publish a correction note. We cannot change the underlying SEF data; that is published by SEF directly.