A multifactorial analysis of the pregnancy outcome in a successful embryo cryopreservation program

To determine which factor, or factors, may influence the success of an embryo-freezing program.

Prospective.

An established, private IVF clinic.

This study comprises data from 185 consecutive thaw cycles (161 patients) that resulted in embryo replacement. The influence of the following factors, with regard to pregnancy outcome, was specifically addressed: embryo quality, day of the endogenous LH surge, number of thawed embryos replaced, length of time frozen, E2 level at the time of the hCG trigger in the stimulated cycle, and patient age at the time of freezing.

An overall pregnancy rate (PR) of 27.6% per ET was achieved in this study. Regardless of the day of the LH surge, patients who had at least one good quality embryo (the "sponsoring embryo") conceived 35% of the time. Patients 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 transfer. None of the 22 patients who were 40 or older conceived. No other factor examined had any effect on pregnancy outcome.

Good quality frozen/thawed embryos are a major factor in achieving a consistently high PR. Poorer quality embryos are capable of implantation but at a significantly reduced rate. Patient age was also found to be significant in predicting pregnancy. Neither the day of the LH surge, number of embryos transferred, length of time frozen, nor the E2 level appears to have any effect on the establishment of pregnancy.