What IVF Clinic Success Rates Actually Mean

A clinic’s success rate is its number of positive results divided by the number of procedures performed so it should be simple to compare clinics. Unfortunately, it is not quite that simple.

There are a number of ways to present the clinic’s data and it’s important you understand the differences when comparing data so that you can determine if you are comparing like for like data. It’s also important you consult the HFEA Choose a Clinic stats. Ultimately you want to know how good the clinic is at getting patients in your age group to have a live birth.

The patient pool  

The first thing to identify is what pool of patients the clinic is using as their base number. It could be:

  • The number of patients who started a treatment cycle

Includes every patient who starts stimulation medication

  • The number of patients who had an egg collection

Does not include people whose cycle was cancelled as they did not respond to the medication or for personal reasons

  • The number of patients who had the embryo transfer

Does not include cancelled cycles or people who had no embryos to transfer due to poor or no fertilisation

  • Per embryo transfer

This examines how many single embryo transfer cycles result in a successful pregnancy as it is a better indicator of the quality and selection of embryos and reduces the risk of a twin or triplet pregnancy

There are arguments for and against each base number, clinics choose the data they feel best reflect their clinical and laboratory ethos and success. But it’s also important for you to know the difference when you compare clinics so that you can make an informed decision.  You should also feel comfortable asking a clinic to explain their success rates in more detail, or asking them for a specific data set you are interested in.

Define Success

The next thing to identify is what the clinic defines as a successful cycle. It could be:

  • A positive urine test, which measures the presence of a pregnancy hormone 12-14 days after embryo transfer
  • A quantitative blood test, which measures the exact level of a pregnancy hormone 12-14 days after embryo transfer
  • A clinical pregnancy, which is ultrasound evidence of a foetal heartbeat 6 weeks after embryo transfer
  • A live birth

The actual numbers and time period

Another thing to consider is the size of the data and timescale being reported. The HFEA requires clinics to have at least 12 months worth of data before publishing.  A good rule of thumb is, the smaller the timescale the smaller the base number of patients covered in the data is. Some things to consider …

  • Is it their most recent available data?
  • Does it cover a year or more of treatment?
  • Does it cover a large number of patients?

Other things to consider

Some clinics have age restrictions or treatment criteria and therefore may not treat women deemed to be poor responders, which will ultimately impact their data.

Some experts also recommend looking at a clinic’s donation programme data. Egg donors are generally all under 35 with good ovarian function, unlike the IVF patient pool. The clinics should do well with these ideal patients and their outcome success should be indicative of their clinical and laboratory techniques and practice.


Now that you have a basic understanding of clinic success rates you should feel more confident looking at the clinic websites. The HFEA requires clinics to display somewhere on their website:

  • Success rates within the past 3 years
  • The Live birth date per cycle started
  • Data should be presented by maternal age
  • The website should include raw patient numbers, not just percentages.

This is good news because it means you should be able to find a uniform set of data so you can compare like for like numbers. If you can’t find that data request it from the clinic as they are required to provide it. It’s important but please remember that there are other factors that impact data such as the patient population. You should feel comfortable, and entitled, to ask questions about a clinic’s success rates.

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