Objective: To review the outcomes of frozen-thawed embryo transfer cycles. Design: Retrospective review. Setting: Tertiary assisted reproduction centre, Hong Kong. Patients: Subfertile patients undergoing frozen-thawed embryo transfer between July 2005 and December 2007. Main outcome measures: Clinical and ongoing pregnancy rates. Results: A total of 983 frozen-thawed embryo transfer cycles performed during the study period were reviewed. The clinical pregnancy and ongoing pregnancy rates were 35% and 30%, respectively. Factors associated with successful outcome included younger maternal age (≤35 years) and 4 or more blastomeres at replacement, but not the method of insemination, the cause of subfertility, or the type of frozen-thawed embryo transfer cycle. The overall multiple pregnancy rate was 18%. For cycles with a single embryo replaced, embryos having 4-cell or higher stages at replacement gave an ongoing pregnancy rate of 25%, whereas those with less than 4 cells had a significantly lower ongoing pregnancy rate of 5% only. Blastomere lysis after thawing significantly reduced the clinical pregnancy and ongoing pregnancy rates of cycles with one embryo replaced. Conclusions Clinical pregnancy and ongoing pregnancy rates of frozen-thawed embryo transfer cycles were 35% and 30%, respectively. Higher pregnancy rates were associated with younger maternal age (≤35 years), blastomere numbers of 4 or more, and no blastomere lysis after thawing.

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