Pregnancy outcome following transfer of human blastocysts vitrified on electron microscopy grids after induced collapse of the blastocoele.

Background: The purpose of this study was to examine the effects on blastocyst survival and subsequent pregnancy rate of 'artificial shrinkage' (i.e. induced collapse of the blastocoele) before vitrification of human blastocysts.

Methods: After embryo transfer in IVF cycles, surplus embryos that developed to the expanded blastocyst stage were cryopreserved. Before vitrification on electron microscopy (EM) grids, artificial shrinkage was induced in expanded blastocysts using a 29-gauge needle. After thawing, transfers were performed on 25 couples. Post-thaw survival rates and clinical outcome after the transfer of vitrified blastocysts were examined.

Results: Of 90 expanded blastocysts vitrified from 25 patients, 81 survived (90.0%) and 40 of them were hatched (49.4%) at the time of transfer. The implantation rate was 29.0% (20/69), and the pregnancy rate was 48.0% (12/25). Nine patients delivered 15 infants, two pregnancies are ongoing and one ended in miscarriage.

Conclusions: The results suggest that artificial shrinkage is a useful technique for vitrification of expanded blastocysts on EM grids.