Understanding IVF Statistics: a Primer

In the United States, IVF centres are required by law to report their statistics to a national register, and the data becomes public information accessible to every existing or prospective patient. The data can, and should, be used to evaluate realistic chances of success and to help differentiate between clinics.

In Canada, there is no requirement that an IVF centre report its own statistics to the public. Clinics do report statistics to CARTR-BORN, which is a national register that computes national statistics. No individual clinic data is reported or released by CARTR-BORN. Clinics tend to post some select statistics, or generalizations about their statistics. More to come about that in my next blog post.

You need to be a bit of a sleuth (or a math major) to understand and evaluate IVF statistics. The most important thing to remember is that statistics can be helpful, but only a physician can help a patient understand the specific likelihood of that patient’s success because the chances of initiating a pregnancy depend on many factors that are personal to the woman undergoing IVF, such as her medical history, age, and BMI, to name but a few.

When reviewing statistics, read the description of the data carefully, and determine the actual statistic being reported. I will help you use the data in my next blog post, but in the meantime, here is a summary of commonly reported categories of statistics:

1. Pregnancy rate per cycle. Translation: how many patients achieved a pregnancy when you factor in all of the transfers that resulted from a single IVF cycle. This statistic will include both fresh transfers and frozen transfers, but also includes statistics taken from cancelled IVF cycles. This can be a helpful statistic as it answers the question: “if I undergo an IVF cycle at this clinic, what are my chances of achieving a pregnancy?”
2. Pregnancy rate per egg collection. Translation: If I undergo an IVF cycle at this clinic, and if eggs are retrieved, what are the changes that I will achieve a pregnancy? This is similar to the pregnancy rate per cycle statistic, but it eliminates all data from cancelled cycles. As a result, this statistic will be higher.
3. Pregnacy rate per transfer. Translation: for every time that one or more embryos were transferred, how many patients achieved a pregnancy? This rate isn’t predictive of your success, as it doesn’t take into account the real possibility of any cancelled cycles, or cycles where retrieved eggs didn’t fertilize.
4. Pregnancy rate per cycle start: Translation: of all the patients who started an IVF cycle, how many achieved a pregnancy? You should also ask how many cycles were cancelled, so you can understand the likelihood of even being able to get to a transfer.
5. Live birth rate per cycle start: Translation: of all the patients who started a cycle in a particular period of time, how many gave birth to a child? This is generally considered to be the gold standard of statistics, but will always be a bit out of date as the clinic can only report statistics after the end of a pregnancy. Clearly, this statistic will be lower than the pregnancy rate per cycle start, as some of the pregnancies will result in miscarriages.
6. Live birth rate per egg retrieval: Translation: for every patient who starts a cycle AND undergoes an egg retrieval, how many gave birth to a child? This statistic will not include all the IVF cycles that are cancelled before the retrieval. Not every cycle started results in an egg retrieval, so this rate tends to be higher than the  live birth rate per cycle start, but lower than the live birth rate per Transfer.
7. Live birth rate per Transfer: Translation: for every time that one or more embryos were transferred, how many patients gave birth to a child? This statistic will appear to be encouragingly high, but is only predictive of your success if you transfer embryos. This statistic does not include all cancelled cycles, or cycles in which eggs were retrieved but embryos failed to grow.

There are other factors to consider, such as how many embryos are being transferred at one time. If the IVF centre heavily favours single embryo transfers, their statistics will be slightly lower than a centre that favours transfers of multiple embryos.  You also need to know how the clinic defines a pregnancy, as the incidents of chemical pregnancy will be higher than pregnancies confirmed by ultrasound examination. The other important piece of information is the number of cycles included in each category. If the sample size is small, the statistics become less meaningful.

Statistics are wonderful tools, but you need to do a bit of homework to be able to use them effectively.