Synchronization between embryo development and endometrium is a contributing factor for rescue ICSI outcome

Recent evidence shows that the outcome of rescue intracytoplasmic sperm injection (ICSI) is unsatisfactory on account of a poor clinical pregnancy rate. These outcomes may be due to either the in-vitro ageing of cultured oocytes before ICSI or the asynchrony between the embryo developmental stage and the endometrial secretory pattern. To address the latter issue, this study performed a retrospective analysis of 534 fresh cycles after rescue ICSI and 64 frozen–thawed cycles in subsequent treatment. Rescue ICSI cycles were divided into three groups: group I included 469 fresh embryo-transfer (FET) cycles; group II included 74 FET cycles in which supernumerary good-quality embryos were also cryopreserved; and group III included 64 frozen–thawed transfer cycles. Group III was considered to have achieved better synchronization than group II. As a result, significantly higher clinical pregnancy (29.69%, 19/64 versus 10.81%, 8/74) and implantation (13.33%, 22/165 versus 5.13%, 8/156) rates were achieved in group III compared with group II (both P < 0.05). Therefore, synchronization of embryo development with the endometrium is considered a contributing factor for rescue ICSI outcome. It is recommended that embryos derived from rescue ICSI cycles should be cryopreserved and subsequently used in frozen–thawed cycles.Intracytoplasmic sperm injection (ICSI) of unfertilized 1-day-old oocytes, called rescue ICSI, has frequently been performed in some infertility centres, when fertilization failure sometimes occurs in conventional IVF cycles. Recent studies showed that the outcome of rescue ICSI was unsatisfactory due to poor clinical pregnancy rates. One reason could be asynchrony between the embryo developmental stage and the endometrial secretory pattern. To address this issue, we performed a retrospective analysis of 534 fresh cycles after rescue ICSI (from January 2006 to January 2011) and 64 frozen–thawed transfer cycles in subsequent treatment (from January 2006 to May 2011) in our infertility centre. In this study, rescue ICSI cycles were divided into three groups. As there was no significant difference in women’s age (31.22 ± 3.38 versus 31.11 ± 3.27 years) between groups II and III, we principally compared these two groups. Group II included 74 fresh embryo transfer cycles, in which supernumerary good-quality embryos were cryopreserved, and group III included 64 frozen–thawed transfer cycles. Group III was considered to have better synchronization than group II. As a result, significantly higher clinical pregnancy (29.69% versus 10.81%) and implantation (13.33% versus 5.13%) rates were achieved in group III compared with group II. Therefore, endometrial synchronization is considered a contributing factor for rescue ICSI outcome and embryos derived from rescue ICSI cycles should be cryopreserved and subsequently used in frozen–thawed cycles.