CRYOCONSERVATION OF HUMAN OOCYTES IN THE PRONUCLEAR STATE IN AN AUTOMATED OPEN SYSTEM

In the period from June 1990 to February 1993, 718 excess pronucleated oocytes from 185 cycles were cryopreserved by using the ''open freezi ng system'' in our IVF-programme at the Department of Gynaecology and Hospital of the University of Bonn. 1.5 mol propanediol and 0.1 mol su crose were used as a cryoprotectant. During this time 287, pronuclear oocytes were thawed; of these 245 survived the freezing process and we re classified as intact. The survival rate in this study was 85.4 %, t hough if only one intact pronuclear oocyte was transferred, no pregnan cy could be achieved, whereas if two or three pronuclear oocytes were transferred, seven to ten pregnancies resulted, respectively (23.3 % a nd 23.8 % pregnancy rates). Eight healthy children have been born to d ate from four other ongoing pregnancies, one of them is a twin pregnan cy.