Clinical factors for successful cryopreserved-thawed embryo transfer

Purpose: To study how clinical factors such as embryo quality, cell stage of embryo at cryopreservation, and synchronization of developmental stages between embryo and endometrium at thawing affect the implantation rate after cryopreserved-thawed embryo transfer (ET), these factors were examined in 106 cryopreserved-thawed ETs including 204 embryos. Results: In 86 embryos graded as high quality before transfer by morphological evaluation, 31 implantations were successful, while the other; low-quality embryos did not implant at all. High-quality embryos received less cryoinjury during cryopreservation compared to the injuries sustained by embryos in moderate and poor quality When cyopreservation was performed at the 1-, 2-, and 3-day cell stages, pregnancies were similarly achieved among most of the embryos at all cell stages. At thawed ETs in natural ovulation cycles, there were some differences among the developmental stages between thawed embryo and endometrium that received the thawed transferred embryos, Although the transfer timelag ranged a day or more, asynchronism of endometrium growth to the cell stage did not reduce pregnancy rates. Conclusions: These results indicated that embryo quality evaluated morphologically was the most important clinical factor for successful implantation of cryopreserved-thawed ET.