Hong Kong Med J 2009;15:420-6 | Number 6, December 2009
Frozen-thawed embryo transfer cycles
William SB Yeung, Raymond HW Li, TM Cheung, Ernest HY Ng, Estella YL Lau, PC Ho
Centre of Assisted Reproduction and Embryology, Department of Obstetrics and Gynaecology, The University of Hong Kong, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong
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.
Key words: Cryopreservation; Embryo transfer; Fertilization in vitro
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