Understanding Success Rates
CDC/NASS publishes fertility treatment outcome data for every reporting clinic in the United States. Here is what those numbers actually measure — and what they do not.
What the numbers mean
The CDC’s National ART Surveillance System (NASS) collects outcome data from fertility clinics that perform assisted reproductive technology (ART) cycles in the United States. Clinics are required by law to report this data annually.
The headline figure you will see on clinic profiles is the live-birth rate — the proportion of treatment cycles that resulted in at least one live-born baby. A rate of 45% means that out of 100 cycles in a given category, roughly 45 resulted in a live birth.
These rates are historical averages for a specific reporting year. They reflect past patients and past clinical protocols, not a prediction for any individual patient.
Denominators: per intended retrieval vs. per transfer
CDC/NASS publishes success rates using two different denominators, and confusing them is one of the most common mistakes in interpreting fertility data.
Live births per intended egg retrieval
This is the more conservative and more informative figure. The denominator includes every patient who started a retrieval cycle — even those whose cycle was cancelled before retrieval, those who retrieved eggs but had no viable embryos, and those who did not proceed to transfer. Because it captures the full cycle journey including failures, this number tends to be lower than the per-transfer rate. It better reflects what patients actually experience when they begin a cycle.
Live births per embryo transfer
This uses only the patients who made it to the transfer step as the denominator. It excludes cycles that were cancelled or produced no transferable embryos. This number tends to be higher than the per-retrieval rate and represents how well transfers specifically succeed, rather than the whole cycle.
When comparing clinics, make sure you are comparing the same denominator type. A clinic with a 50% per-transfer rate and a clinic with a 35% per-intended-retrieval rate are not necessarily comparable without additional context.
Age cohorts
CDC/NASS breaks success rates down by patient age. This is critically important because age is the single most significant factor in ART outcomes when using a patient’s own eggs. Standard cohorts include:
- Under 35
- 35–37
- 38–40
- 41–42
- 43 and older
A clinic’s overall average is heavily influenced by the age mix of its patient population. A clinic that sees a higher proportion of younger patients will naturally show higher overall rates than an identical clinic that treats more patients over 40 — even if the clinical protocols and outcomes within each age cohort are identical. Always compare within the age cohort most relevant to you.
Donor eggs vs. own eggs
CDC/NASS reports success rates separately for cycles using the patient’s own eggs and cycles using donor eggs. These are fundamentally different populations:
- Own-egg cycles are strongly age-dependent. Rates decline meaningfully with patient age due to egg quality.
- Donor-egg cyclesare primarily dependent on the donor’s age and are much less sensitive to the recipient’s age. Success rates in this category tend to be higher and more consistent across age groups.
Mixing own-egg and donor-egg outcomes into a single headline number obscures both populations. Explore Fertility displays them separately where CDC/NASS data permits.
Why you see “Suppressed” or “Insufficient data”
CDC/NASS suppresses or flags small-sample results to protect patient privacy and to prevent misleading statistics:
Neither value should be interpreted as a negative outcome signal for the clinic.
Reporting lag
CDC/NASS data is published roughly 18–24 months after the end of the reporting year. The 2022 dataset, for example, was published in 2024. This means the success rates you see on clinic profiles reflect protocols, staff, and equipment from the reporting year — not necessarily today’s clinic. Clinics can and do change in meaningful ways over two years.
We always display the reporting year alongside success-rate data so you know which cohort is being described.
Why a clinic’s number is not its quality score
Success rates as reported by CDC/NASS are aggregate statistics, not clinic quality scores. Many factors outside clinical skill affect a clinic’s reported rate:
- Patient age mix and case complexity
- Patient selection — some clinics accept higher-risk cases than others
- Volume — clinics with very few cycles in a cohort show more variance
- Whether a clinic transfers single or multiple embryos
- The proportion of fresh vs. frozen embryo transfers
- Reporting accuracy
A clinic with a higher rate is not necessarily better for your specific situation. Discuss success rates with a reproductive endocrinologist who can interpret them in the context of your diagnosis and treatment plan.
Source dataset
All success-rate data on Explore Fertility originates from the CDC/NASS public dataset. You can explore the full dataset, including national averages and clinic-level breakdowns, directly on the CDC website.
View CDC/NASS source dataset