Just like with the costs you should not rely entirely on the success rates the clinic shares with the patients on their website or pamphlets. Success rates in each clinic could look different in a different clinic.
There are a lot of factors which influence success rates like the medical status of the patient, cause of infertility, the quality of donor eggs and the IVF procedure itself. Additionally technology and equipment and the experience of the medical team are also important factors.
Like it was said before, success rates can be different for each patient and your success rate depends on your individual situation and medical status. IVF clinics usually report their statistic data to the European Society of Human Reproduction and Embryology (ESHRE) but this is not an obligatory procedure.
Looking at the percentage of the success rate is however not enough because you need to look additionally at the number of cycles a clinic has done on a specific year. One clinic could have a 65% success rate but in a year where they had only 300 cycles done. In comparison another clinic could have a lower success rate of 61% but with a significantly higher amount of cycles done for e.g. 1500. Furthermore you should take under the consideration on the state of the patients that were undertaking the treatment. The clinic with the better success rate could for example have done more treatments on younger women than in the clinic with a lower success rate which had older patients. In such case if you are older it probably would be better to choose the clinic where the success rates were slightly lower but they have better experience with older patients.
You not only need to remember about the age of the patients but also about the fact that in some clinics they still transfer multiple embryos while in other they have a single embryo transfer policy. This can also have a significant impact on the resulting success rates. Single embryo transfer is considered safer because of eliminating the chance of multiple pregnancy at the cost of success rates. In another clinic you can have a higher success rate but with a multiple embryo transfer which rises the chance of multiple birth and the complications connected to it like miscarriage or a too early birth.