In Vitro Fertilization

Interpreting IVF Success Rates

What does it mean if you are told that a program has a 50% pregnancy rate? Is this for all cycles or just a recent group? Does this refer to all initiated cycles or only those that are attained after an embryo transfer? Does this mean live deliveries or does it include miscarriages and "biochemical" pregnancies? Does the program accept older women and couples with a severe sperm abnormality? Clearly a good grasp of the components of an IVF cycle is critical to a true understanding of the complex statistics provided by different programs.

Initiated cycles refers to all attempts at ovulation induction with the intent to perform an IVF cycle. If the response to this stimulation is sub-optimal then cancellation of the cycle may occur before an egg retrieval is attempted. Some programs will not accept older women or men with a severe sperm abnormality. These couples are more likely to have cycles cancelled due to failure of ovulation induction and fertilization respectively. We accept women over the age of 40 as long as they have adequate ovarian function. We accept men with severe abnormalities and have been very successful even with sperm counts of less than 1,000 per cc with poor motility.

Retrievals refer to the actual attempt to obtain the eggs. In order to get to the stage of embryo transfer, a successful egg retrieval has to be performed and fertilization and initial embryo development must occur in the laboratory. A clinical pregnancy refers to the identification of a pregnancy sac in the uterus, not just a positive pregnancy test. Unfortunately, miscarriage may still occur later. It is therefore important to consider the live delivery rate. Two frequently used statistics need to be clearly identified and understood:

The delivery rate per retrieval provides insight into the likelihood of having a baby when a retrieval is performed. This is of more practical importance to patients than the other statistic of clinical pregnancy rate per embryo transfer. The clinical pregnancy rate does not take the likelihood of miscarriage into account, cycles cancelled before retrieval or due to failure of fertilization. The clinical pregnancy rate per embryo transfer does, however, provide a good insight into the quality of a program and is frequently used in the medical literature.

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