What’s the difference between cumulative success rates and success rates per embryo transfer?

When we talk about success rates in fertility treatments, we need to make sure that we exactly know what we are talking about. Patients would use success rates to compare fertility treatments and fertility clinics before deciding on where to undergo their own fertility treatment. Of course, the goal of any fertility treatment is having a healthy baby at home so the most important success rate would be simply a healthy baby at home or the newborn rate. But of course, from a medical point of view, we will use other success rates to compare the results of different fertility treatments. We have a pregnancy rate, which is having a positive pregnancy test. We also have a viable pregnancy rate, which means having a normal pregnancy that would exclude ectopic pregnancies and miscarriages.

So when we are looking at success rates per treatment, we need to make sure if we are talking about a baby at home, a viable pregnancy, or a positive pregnancy test. When also need to make sure if we are talking about success rates per transfer or started treatments. During treatment, we might need to cancel the cycle for different reasons, such as no follicle growing under ovarian stimulation, no oocytes after pick up, or no mature oocytes.

Sometimes fertilization will fail, and we won’t have any embryos. And even if we have day 5 embryos, sometimes the cycle has to be cancelled because they’re not high-quality blastocysts, or they’re abnormal from a chromosomal point of view. So it is very important. If we are talking about success rates per transfer – when a patient finally has a high-quality blastocyst to transfer – or success rates every time we start treatment.

Finally, we need to explain the difference between a pregnancy rate per transfer and a cumulative pregnancy rate. The pregnancy rate per transfer is the chance of having a positive pregnancy test after a single transfer. The cumulative pregnancy rate refers to the results after transfers of all the embryos we had from one ovarian stimulation. It may include fresh embryo transfer and sometimes also thawed embryo transfer from the same ovarian stimulation. If after the transfer of a high-quality day-5 embryo, we have a pregnancy rate of up to 65 % and still one frozen embryo to transfer, the cumulative pregnancy rate may rise to 85-86%. And if afterwards we still have a third embryo to transfer, this pregnancy rate might be over 90%.

So when we compare results, we need to make sure if we are talking about pregnancy rates per transfer or cumulative rates for the whole fertility treatment cycle.

What does the cumulative pregnancy rate mean? Actually, around 30% of patient burn-out after unsuccessful IVF is mainly associated with emotional and physical burn-out, the poor chances of success after continued treatment, and financial expenses. To facilitate the assessment of the chances of a successful outcome, the term ‘the cumulative live birth rate’ has been implemented. The term ‘cumulative’ is derived from the Latin word ‘cumulare’ (‘to accumulate’).

According to the actual definition, the cumulative pregnancy rate takes account of all pregnancies achieved by successive several embryo transfers, irrespective of whether these embryos are derived from the so-called fresh cycles or frozen-thawed embryo transfers.

Interestingly, the cumulative pregnancy rate also implies that the chances of getting pregnant increase with the number of received therapy cycles. The decision of whether a woman should start a continued IVF treatment should belong to both a fertility specialist and a patient who are assessing all medical and non-medical issues.

The most crucial change in the assisted reproduction in the last years has been vitrification.

Nowadays, we have the same chance of pregnancy when transferring fresh embryos or frozen embryos. This has made us change the nomenclature of the pregnancy chances. A few years ago, we talked about a pregnancy chance when we transferred one fresh embryo. Nowadays, we talk about a cumulative pregnancy chance when we count all the transferred embryos: both fresh and frozen.