Effectiveness of different protocols for slow freezing of human blastocysts

Background: Pregnancy rate after the transfer of frozen / thawed human blastocysts has been lower in comparison with the pregnancy rate in in vitro fertilization (IVF) cycles with fresh embryos. There is a need for the optimization of freezing protocols. Conclusions: All freezing protocols using a simple freezing medium were more effective than protocol with a complex medium. Their application in IVF patients with frozen surplus blastocysts (these patients delivered in fresh cycles in 51.4 %) increases the cumulative delivery rate by an additional 15.2 % with every thawing cycle. The morphology of blastocysts and cycle preparation for transfer had the strongest influence on the success of freezing programme.