You open two clinic websites and see 60% at one and 40% at the other. It looks like a verdict. It usually isn't. Most of the gap comes from what each number measures and who it measures, not from a simple difference in quality.
According to SART's 2023 national summary, what was the live birth rate per intended egg retrieval for women under 35 using their own eggs?
Select one answer.
The biggest driver is who the clinic treats
Age is the single most important factor in IVF outcomes when a patient uses her own eggs. SART states plainly that the major predictor of an IVF cycle's outcome is age at the time of egg retrieval, because egg number and quality decline over the reproductive years, and miscarriage risk rises — particularly above age 40 (SART success rates guide).
That matters because clinics serve different populations. A practice drawing many patients under 35 will post higher headline numbers than one whose patients skew older, even if both labs perform equally well. Diagnosis matters too: age and diagnosis affect outcomes more than almost any other factor, and patient populations differ from clinic to clinic (SpringCreek Fertility).
The national data shows how wide the age effect is. In SART's 2023 national summary, live births per intended egg retrieval using a patient's own eggs were 53.2% for women under 35, 39.9% for ages 35–37, 26.2% for 38–40, 13.2% for 41–42, and 4.1% above 42 (SART national summary). A clinic's mix of these bands can move its headline rate enormously.
The denominator changes the answer
A success rate is a fraction: live births divided by something. That "something" can be intended retrievals, actual retrievals, or embryo transfers — and each choice produces a different percentage from the same clinic and year (Fertility Institute).
This is why a clinic's website might advertise 60% while its official report for the same year shows closer to 40%. Neither is necessarily wrong; they answer different questions. The same source notes that "success" itself is defined differently across reports — a positive pregnancy test in one, a live birth in another.
Live birth rate is the most meaningful endpoint because it reflects an actual baby, but it takes longer to confirm. Because full-term delivery data takes time to collect, published figures lag roughly 16 months or more behind the year being reported (RSC Bay Area). A strong year in old data is not the same as a current pattern.
Donor eggs and sample size distort comparisons
Whether donor-egg cycles are folded into a headline figure changes what the number means. Donor-egg outcomes differ from own-egg outcomes, so mixing them inflates or muddies the rate depending on the mix.
Sample size is the quiet variable. A rate built on a handful of cycles is far shakier than one built on hundreds, but the headline rarely shows the denominator. Research on clinic volume found that average live birth rates from IVF are not affected by increasing cycle volume per clinic, but there is greater variability in success rates at some volumes (Fertility and Sterility, 2021). In plain terms: small numbers bounce around more.
A checklist for comparing two clinics fairly
- Match your age band. Pull the rate for your age group, not the all-ages headline.
- Confirm the endpoint. Is it a positive pregnancy test, a clinical pregnancy, or a live birth?
- Find the denominator. Intended retrievals, actual retrievals, or transfers?
- Check donor eggs. Are donor-egg cycles included or reported separately?
- Note the year. Old data may not reflect current practice.
- Weigh the sample. Ask how many cycles the figure is built on.
- Expect reconciliation work. Different official formats can show figures that look inconsistent for the same clinic; that is often a reporting artifact.
- Weigh what the rate can't capture. The doctor relationship, the lab, the cost, and how a clinic handles a failed cycle are not in the percentage.
What to ask at a consultation
Bring the specific figure you saw and ask which age band, diagnosis group, year, and denominator produced it. Ask whether donor-egg cycles are included and how many cycles the rate represents. Then ask for the clinic's own data for patients like you. A rate that doesn't describe your age and diagnosis is answering a different question than the one you're asking.
How the Featured Expert Can Help
Fertility X-Ray provides detailed, plain-English reports on U.S. fertility clinic success rates, turning CDC data into actionable dossiers for patients. It sells individual clinic reports and comparative analyses for a fee, aiming to help prospective patients make informed choices. If you want help reading a clinic's numbers before a consultation, you can explore the reports at Fertility X-Ray.