Implementation of blastocyst transfer in IVF

The current thesis represents the sequence of several studies concerning the transfer of embryos at the blastocyst stage in IVF and whether this has implications on the probability of achieving a pregnancy. In young patients, it was shown that a single blastocyst transfer significantly increases the probability of pregnancy and birth of a child compared to single cleavage-stage embryo transfer. Similarly, it was demonstrated that once a patient has at least four morphologically good embryos on the third day of embryo culture, extending culture to day 5 and transferring two blastocysts, results in a significantly higher live birth rate. As plausible explanations, it was proposed a better genetic euploid status of survived embryos reaching the blastocyst stage and a better synchronization with endometrium at the site of implantation. The latter seems to be distressed by steroid levels and especially progesterone at the late follicular phase. Nevertheless, the fragmentation rate and the developmental stage of an advanced blastocyst quantitated by a systematic scoring system, affects its implantation potential. Finally, a meta-analysis of published studies indicated a significant trend towards higher delivery rate, when blastocysts are utilized for embryo transfer.