← Articles

IVF success rates: what does that percentage actually measure?

Before comparing two percentages, match the outcome, patient group and starting point. "Success per transfer" is not the chance of a baby from starting IVF.

CDC warns that clinic rates reflect different patients and treatment methods, not any one person's chance of success.

Check what counts as success

A positive test, a pregnancy seen on ultrasound and a live-birth delivery are different outcomes. Ask which one the clinic is quoting.

Then ask what the percentage is divided by:

• Intended retrievals: cycles started with the plan to retrieve eggs.
• Actual retrievals: cycles that reached retrieval of at least one egg.
• Transfers: procedures that reached the point of transferring an embryo.

These are different CDC measures. A transfer-only rate leaves out people who did not reach transfer. It cannot answer the whole-cycle question by itself.

One pathway can produce two honest percentages

For illustration only, imagine 100 treatment starts, 80 transfers and 40 live-birth deliveries in the same defined follow-up period. That is 40 ÷ 100 = 40% per start and 40 ÷ 80 = 50% per transfer. These are invented counts to explain the denominator, not a clinic's results or a prediction.

Neither percentage needs to be false. But presenting the 50% figure as your chance from starting treatment would leave out those who did not reach transfer. The same caution applies when a clinic reports only selected embryos or only one transfer: ask which patients and attempts are missing from the quoted number.

Match the patients and the follow-up

Compare own eggs with own eggs, and donor eggs with donor eggs. Match the age group. Ask whether a quoted rate includes everyone in that group or only selected embryos, such as tested embryos.

If the rate is cumulative, ask which transfers and how much follow-up it includes. CDC's cumulative own-egg clinic rates include transfers within one year after retrieval; not every other report must use that same window.

Check the reporting year and whether results are preliminary. Published outcomes describe the patients treated in that period, not a live reading of today's clinic.

Also look at the number of cycles behind an age-group rate. A percentage without its cohort size hides how much information it contains. Do not assume that a better headline, or a rate from an older reporting year, proves the current lab is better for you. Ask the team to explain case mix and the patients it treats before making a costly change of clinic or moving stored embryos.

Bring the clinic a better question

"For people with my age and treatment history, what is the chance of a live birth from starting a retrieval, including later transfers? Which group are you using, and what might make my outlook different?"

Ask for the report behind the answer. If a number is missing, ask why; do not read a blank as zero.

You can use CDC's clinic reports as a starting point. Use the consultation to understand differences, not to turn one headline percentage into a league table.

Questions about the lab and treatment plan →

Last updated: November 6, 2026