Blastocyst transfer

The rationale for blastocyst culture (day 5 or 6) is to improve both uterine and embryonic-synchronicity and enable self-selection of embryos, thereby resulting in higher implantation rates. The question is whether blastocyst transfer improves live birth rate and other associated outcomes compared with cleavage-stage (day 2 or 3) embryo transfers. From the results of 23 randomized controlled trials (RCTs), there was no difference in clinical pregnancy rate between early cleavage and blastocyst transfer. The four RCTs that reported cumulative pregnancy rates significantly favored early cleavage transfer. In the 12 RCTs that reported live birth rates, the difference was significantly in favor of blastocyst culture. The typical live birth rate in clinics that use early cleavage-stage cycles is 31%, which would increase to 42% if blastocyst transfer was used. In the German IVF register (DIR), the pregnancy rate is slightly higher after blastocyst transfer, but at the expense of an increased rate of multiple pregnancies.