Exposure time to cryoprotectants influences oocyte survival rate NIKOS TSAGIAS1*, BASIL TARLATZIS2, EYTHALIA PAGGOU1, THOMAI SANOPOULOU1, ELISAVET XATCHIOANNOU1, ALEKA TOKMAKIDOU1, MINAS ARSENAKIS3 and IOANNIS BONTIS1 1 Infertility and IVF Center, Geniki Kliniki, Thessaloniki 54645, Greece 2 Unit for Human Reproduction, First Department of Obstetrics and Gynecology, School of Medicine, Aristotle University, Thessaloniki 54124, Greece 3 Department of Genetics, Development & Molecular Biology, School of Biology, Aristotle University, Thessaloniki 54124, Greece Abstract Oocyte cryopreservation may have significant potential for assisted reproductive technology. The success depends on morphological and biophysical factors. The main biophysical factor affecting human oocyte survival is the intracellular ice formation which generally pierces the membranes causing cell lysis. Intracellular ice formation can be affected by the presence of cryoprotectants in the freezing solutions. Thus, the aim of this study was to examine the effect of the exposure time to cryoprotectants on human oocytes before freezing. Oocytes were cryopreserved in 1,2 propanediol added to sucrose, using a slow-freezing-rapid-thawing method. Exposure time longer than 5 min to cryoprotectant solutions, before lowering of the temperature, significantly increased the oocyte survival rate. These data are also supported by morphological parameters, e.g. ooplasm size and perivitelline space. Adequate oocyte dehydration should be obtained before lowering of the temperature and this can be achieved by sufficient exposure to cryoprotectants. That could further contribute to avoiding of formation of cytoplasmic ice crystals, which are the main factor influencing oocyte survival rate during cryopreservation.   < back .