Vitrified-Warmed Blastocyst Score Effects Pregnancy Outcomes: Towards a Single Blastocyst Vitrification and Transfer

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No a referable quality selection criteria for a single vitrified-warmed blastocyst transfer. Therefore, the present study aimed to investigate the relationship between vitrified-warmed blastocyst score and clinical pregnancy outcomes. This retrospective analysis consisted of 221 patients undergoing two blastocysts transfer on thawing day. Implantation rate, fetal heart pregnancy rate, live-birth rate, multiple birth rate were analyzed. When a patient received two high-quality vitrified-warmed blastocysts (=3BB), implantation rate and fetal heart pregnancy rate were 48.2% and 65.5%, respectively. The multiple birth rates in this group were 44.4%. When two vitrified-warmed blastocysts (one =3BB and another <3BB) were available for transfer, implantation rate and fetal heart pregnancy rate were 34.5% and 52.7%. The multiple birth rate for this group was 29.6%. When only two generalquality vitrified-warmed blastocysts (<3BB) were transferred, implantation rate and fetal heart pregnancy rate were 21.7% and 35.9%, and the multiple birth rate was 21.7%.

The ability to transfer one good-quality vitrified-warmed blastocyst (=3BB) should lead to fetal heart pregnancy rates greater than 52% and live birth rates greater than 36%. Results of the present study can provide guidelines for a single vitrified-warmed blastocyst transfer, which is an effective means of eliminating multiple gestations and avoiding the complications associated with such pregnancies. Multiple pregnancies are a complication of human Assisted Reproductive Technology (ART), rather than a successful result. So, how to reduce the multiple pregnancy rates and maintain the acceptable overall live-birth rate have become research hotspots in the area of reproductive medicine. The strategy of a single embryo transfer is the most effective way to achieve single pregnancy.

Transfer of an embryo with a high potential for development and implantation is a key success factor in ART. Routine blastocyst culture using sequential culture media in vitro can make a better assessment for embryo viability and may confer a selection advantage. Moreover, blastocyst transfer has been associated with a higher implantation rate and a better synchronization between endometrial receptivity and embryo. In a conventional In Vitro Fertilization (IVF) cycle, the use of exogenous gonadotropins results in Ovarian Hyper Stimulation Syndrome (OHSS). Cryopreservation programs are essential for patients who suffered from OHSS. Moreover, for infertile women with the polycystic ovary syndrome, frozen-embryo transfer was associated with a higher rate of live birth and a lower risk of the OHSS than fresh-embryo transfer after the first transfer, because vitrified- warmed blastocyst transfer occurs within a uterine environment that more closely resembles spontaneous conception. In addition, cryopreservation process is used for the storage of supernumery embryos to increase cumulative pregnancy rate.