Why You Can't Line Up Two Clinics Side by Side

Can you compare two clinics' success rates directly?

Not in the way the numbers invite. Every US fertility clinic reports its cycles to the same federal system, and both the CDC and SART publish the results 1Ref 1Centers for Disease Control and Prevention (2024).ART Success Rates.Every US ART clinic is required by federal law to report its cycles, and the CDC publishes national and clinic-level success-rate data — the shared reporting behind both clinics' numbers, though it is not built to rank them. — but that shared reporting does not make two clinics' rates interchangeable. A success rate is not a standardized test score. It is shaped by who the clinic treats, which cycles it counts, and how it does the arithmetic, and those differ from clinic to clinic.

So the honest answer to whether you can line these two up is: not to decide which is better. You can read each clinic's data to understand what it does and whether its patients resemble you. What you cannot do is treat the higher percentage as the better clinic — often it is simply the clinic with the easier patients.

Case mix is the biggest reason

The largest single distortion is case mix. Case mix is the mix of ages, diagnoses, and prognoses among the patients a clinic accepts. A program that welcomes older patients, poor responders, and complex referrals will post a lower rate than one that quietly steers those patients away, even if the first clinic is the more skilled. The number went down because the patients were harder, not because the care was worse.

This is the core reason clinic success rates mislead when read as a ranking. SART reports outcomes broken out by patient age band precisely because a single blended percentage hides who was actually treated 2Ref 2Society for Assisted Reproductive Technology (SART) (2024).National Summary Report (SART CORS Online).SART reports IVF outcomes broken out by patient age band and by cycle, and its data is meant for national aggregate understanding rather than as a single named clinic's marketing claim.. When you look at a rate, the first question is not how high it is but for whom — what a good success rate is depends entirely on the age and diagnosis of the patients behind it.

The denominator changes the answer

Even for identical patients, the same cycle can yield very different percentages depending on what sits in the denominator. A rate per embryo transfer looks higher than a rate per cycle started, because cycles that never reached transfer have been removed from the bottom; a rate per patient counts people rather than attempts. The federal methodology defines each of these measures and warns that the national figures are noncumulative — they describe one reporting year, not lifetime odds 3Ref 3Centers for Disease Control and Prevention (2024).NASS Technical Notes.The CDC's National ART Surveillance System methodology defines how cycles are counted and how success measures are constructed, and explains that national figures are noncumulative and that small clinics' rates swing on few cycles..

Two clinics may not even be quoting the same denominator when they market themselves. One advertises its best-looking per-transfer number; the other quotes a more conservative per-cycle figure. Comparing them directly is comparing two different fractions. Always find the phrase attached to the percentage before you let it mean anything.

Cherry-picking and unproven add-ons

Beyond the federally reported data, a clinic controls the story it tells on its own website, and that story can be curated. Cherry-picked cycles — reporting only a favorable subgroup, or canceling poor-prognosis cycles before they would count — can lift an advertised rate without any change in skill. So can leaning on add-ons that promise higher success. Many marketed IVF add-ons, from certain genetic screens to assisted hatching, lack good evidence of benefit; the UK regulator rates most of them as unproven and some as potentially harmful 4Ref 4Human Fertilisation and Embryology Authority (2024).Treatment add-ons with limited evidence.The UK regulator's color-coded ratings find that most marketed IVF add-ons lack good evidence of benefit and some may cause harm, so a clinic's higher advertised rate is not evidence that its add-ons work..

Refund and multi-cycle packages add their own pressure. Reproductive-medicine ethics guidance holds that such programs are acceptable only when the clinic discloses its own success rate and defines success in advance 5Ref 5Ethics Committee of ASRM (2023).Financial "risk-sharing" or refund programs in assisted reproduction: an Ethics Committee opinion.ASRM ethics guidance holds that refund and risk-sharing programs are acceptable only when success is defined in advance and clinic-specific success rates are disclosed, and it flags the conflict of interest that can push clinics toward easier cases. — but the same structure gives a clinic a reason to select easier patients, which quietly flatters its numbers. A higher rate can reflect marketing choices, not better medicine.

Small samples and clinic volume

A percentage built from a handful of cycles is mostly noise. A smaller clinic's rate can swing widely from one year to the next on a few good or bad outcomes, so a gap between two clinics may be statistical chance rather than a real difference 3Ref 3Centers for Disease Control and Prevention (2024).NASS Technical Notes.The CDC's National ART Surveillance System methodology defines how cycles are counted and how success measures are constructed, and explains that national figures are noncumulative and that small clinics' rates swing on few cycles.. This is one place the federal caution against ranking clinics bites hardest: the uncertainty around a small clinic's number is wide.

Clinic volume is worth understanding for this reason, but not as a simple bigger-is-better rule. A high-volume program produces more stable statistics and often more experience with unusual cases; a lower-volume clinic is not automatically worse, but its published rate carries more uncertainty. Asking how many cycles like yours a clinic performs each year tells you both how experienced it is and how much to trust its numbers.

So is comparing ever useful?

None of this means the data is useless for choosing — only that it is useless as a scoreboard. There is a fair way to hold two clinics' reports side by side: not to crown a winner, but to compare how each behaves. Does each break its results out by age and diagnosis? Does each explain its denominators plainly? Does each report a healthy single-embryo-transfer practice? Those are process signals you genuinely can line up 2Ref 2Society for Assisted Reproductive Technology (SART) (2024).National Summary Report (SART CORS Online).SART reports IVF outcomes broken out by patient age band and by cycle, and its data is meant for national aggregate understanding rather than as a single named clinic's marketing claim..

Used that way, the exercise rewards honesty rather than the highest percentage. A clinic that shows you its age-specific numbers, names its denominators, and matches its reported patients to your situation is easier to trust than one waving a single large figure — even if that figure looks better at a glance. The comparison you can make fairly is of transparency and fit, not of who is best.

What to read instead

Since the rankings do not hold up, aim the data at a better question: not which clinic wins, but what your realistic odds are and whether a clinic fits you. The CDC's IVF Success Estimator gives an individualized live-birth estimate from national data based on your age, height and weight, and diagnosis, for ages 20 to 50 6Ref 6Centers for Disease Control and Prevention (2024).IVF Success Estimator.The CDC's IVF Success Estimator returns an individualized live-birth estimate from national data based on age, height and weight, and diagnosis, for ages 20 to 50, reflecting national averages rather than any single clinic's results.. It reflects the national average rather than any one clinic, which is exactly why it is a fairer starting point than a marketing percentage.

From there, use the specifics you can actually verify:

• Match the reported patients to yourself. Read each clinic's data for your age band and diagnosis, not its blended headline.
• Bring questions to the table. A short list of first-consult questions — about denominators, single-embryo-transfer practice, and add-ons — reveals more than any percentage.
• Look past the number. When you research a fertility clinic near you, weigh the embryology lab, communication, and how honestly the clinic explains its own data.

The clinics worth choosing are usually the ones willing to tell you why their number is what it is.