A MULTIFACTORIAL ANALYSIS OF THE PREGNANCY OUTCOME IN A SUCCESSFUL EMBRYO CRYOPRESERVATION PROGRAM

Objective: To determine which factor, or factors, may influence the su ccess of an embryo-freezing program. Design: Prospective. Setting: An established, private IVF clinic. Patients: This study comprises data f rom 185 consecutive thaw cycles (161 patients) that resulted in embryo replacement. The influence of the following factors, with regard to p regnancy outcome, was specifically addressed: embryo quality, day of t he endogenous LH surge, number of thawed embryos replaced, length of t ime frozen, E2 level at the time of the hCG trigger in the stimulated cycle, and patient age at the time of freezing. Results: An overall pr egnancy rate (PR) of 27.6% per ET was achieved in this study. Regardle ss of the day of the LH surge, patients who had at least one good qual ity embryo (the ''sponsoring embryo'') conceived 35% of the time. Pati ents who lacked a sponsoring embryo frozen conceived 15% of the time. Patients who were 39 years of age or younger had a PR of 31% per trans fer. None of the 22 patients who were 40 or older conceived. No other factor examined had any effect on pregnancy outcome. Conclusions: Good quality frozen/thawed embryos are a major factor in achieving a consi stently high PR. Poorer quality embryos are capable of implantation bu t at a significantly reduced rate. Patient age was also found to be si gnificant in predicting pregnancy. Neither the day of the LH surge, nu mber of embryos transferred, length of time frozen, nor the E2 level a ppears to have any effect on the establishment of pregnancy.