There are many ways in which IVF statistics can be presented. Be aware that data in any form can be shown to put things in the most favorable light. A few things to keep in mind are:
The Society for Assisted Reproductive Technology (SART) has set the following guideline:
"The preferred way to avoid misleading patients is to report live birth data per cycle initiated and per egg retrieval procedure"
Practice Committee Report: Guidelines for Advertising by ART Programs, Jan. 1998
When rates are stated per cycle initiated, every patient who enters that clinic’s IVF program is included in the results. Per egg retrieval includes only those patients who actually underwent oocyte retrieval. (Some women are dropped from the cycle prior to that point due to lack of adequate response to the ovulation-induction medication.) SART considers both of these to be realistic: e.g., what is your likelihood of success if you enter their IVF program (by beginning the medications) and what is your likelihood of success if you actually undergo the egg retrieval procedure?
If an infertility clinic states its results per embryo transfer (a method not recommended by SART) they are including in their patient group only those whose embryos successfully fertilized. Therefore, an IVF program can have relatively poor results with their medication protocols and/or fertilization rates, yet have high success rates per embryo transfer.
A chemical pregnancy refers to all women who had a positive pregnancy test following their IVF cycle. Clinical pregnancies refers to women whose positive pregnancy tests were followed by identification of a fetus on ultrasound at about seven weeks gestation. Some miscarriages can be expected at that point and therefore the live birth rate generally will be lower than the clinical pregnancy rate. Since you presumably want to know what your chances are of having a baby (not just becoming pregnant) from IVF, live birth data will give you a better picture than clinical pregnancy rates.
An ongoing pregnancy is different from a clinical pregnancy in that it is one which has reached the second trimester and is therefore quite likely to result in a live birth. It is considered acceptable to state ongoing pregnancies in place of live births when quoting statistics from recent IVF cycles, in which some of the patients are still pregnant and the live birth rate is, thus, not known.
Before you consider an IVF clinic’s success rates, it is important to note how they arrive at their rates. Are they quoting clinical pregnancies or live births, rates per initiated cycle or per oocyte retrieval?
Further, make sure the IVF program is including all of their data. For example, if they quote statistics only for "under 40" patients, the numbers will most likely be higher than if they include all age groups. And be sure that a program is presenting all their data, not just the selected months or years that they want you to see.
Note, also, whether the data has been reported to (and thus verified by) SART.
No Comparison is Truly Accurate
Even armed with this knowledge, there is no way to truly compare one IVF clinic with another. Some will exclude potential IVF patients whose medical histories indicate that they are unlikely to succeed. These IVF clinics will appear to have better success rates than those who accept everyone who comes to them for help. Also, some may have more success with couples who have your particular condition than do others. The SART guidelines (Practice Committee Report: Guidelines for Advertising by ART Programs, January 1998) specifically caution their member clinics to make consumers aware that "as entry level criteria are highly variable for each program, a center-by-center comparison of results is not valid."