As a result, success rates for 1998 may differ from current rates. No reported success rate is absolute. A clinic s success rates will vary from year to year even if all determining factors remain the same. However, the more cycles that a clinic carries out, the less the rate is likely to vary. Conversely, clinics that carry out fewer cycles are likely to have more variability in success rates from year to year.
Some clinics see more than the average number of patients with difficult infertility problems.
Some clinics are willing to offer ART to most potential users, even those who have a low probability of success. Others discourage such patients or encourage them to use donor eggs, a practice that results in higher success rates among older women. Clinics that accept a higher percentage of women who previously have had multiple unsuccessful ART cycles will generally have lower success rates than clinics that do not. In contrast, clinics that offer ART procedures to patients who might have become pregnant with less technologically advanced treatment will have higher success rates than clinics that do not. A related issue is that success rates shown in this report are presented in terms of cycles, as required by law, rather than in terms of women.