Successful pregnancy after recryopreservation by vitrification of one blastocyst developed from a frozen embryo obtained by PESA: case report

Excerpt

The cryopreservation of human embryos in different cleavage stages has been employed as part of assisted reproduction technologies (ART), as it allows the transfer of less embryos and increases the cumulative gestation rate of a couple. Human embryos can be cryopreserved by slow or ultra-rapid freezing and vitrification. For decades, human embryos have been successfully cryopreserved using the slow rate or equilibrium freezing protocols at the 4–8 cell stage and more recently at the blastocyst stage. The freezing process includes ice crystals formation and osmotic and chilling injury, factors that may lead to damaged blastomers and zona pelucida resulting in low embryo survival. On the other hand, vitrification eliminates ice crystals formation and most protocols are very simple to perform. However, some authors consider vitrification an experimental method in human reproduction, largely because of its inconsistent reported survival rates and the variety of solutions, vessels and carriers employed [1]. A meta-analysis and systematic review found that vitrification is superior to slow freezing, which in turn is superior to ultra-rapid freezing [2] and it may be employed as an effective cryopreservation alternative to slow freezing, provided that technical and methodological details of this technique are carefully observed. …