Vitrification of cleavage stage embryos and blastocysts in ART practice

The importance of cryopreservation in ART steadily increased over the last decades due to the introduction of single embryo transfer to avoid high risk multiple pregnancies. The general aim of this thesis was to optimize the cryopreservation program for cleavage stage embryos (day 3) and blastocysts (day 5/6) at the Centre for Reproductive Medicine (CRG) of UZ Brussel. Vitrification using a closed high security device was implemented in our IVF centre in 2008 for blastocysts and in 2010 for cleavage stage embryos in order to improve the efficiency of our cryopreservation program in terms of embryo survival (and quality) on the one hand and implantation rate on the other hand. The outcome of the first two years of blastocyst vitrification was evaluated. It was concluded that vitrification was successful for blastocysts with or without blastomere biopsy on day 3. To further improve the results of the blastocyst vitrification program, a randomised controlled trial aimed to investigate the effect of laser-induced artificial shrinkage on survival, quality and implantation potential of vitrifiedwarmed blastocysts. It was concluded that applying artificial shrinkage before vitrification further increased the efficiency of the vitrification program. For day 3 cleavage stage embryos, the consequence of postwarming cellular loss for the further developmental potential of multicellular embryos was investigated and compared for the existing slow freezing (DMSO) protocol and the newly introduced vitrification method. Vitrified day 3 embryos showed higher survival rates and better development after overnight culture than slowly frozen embryos, regardless of the number of cells lost.