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 freezing 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 sucrose were used as a cryoprotectant. During this time 287, pronuclear oocytes were thawed; of these 245 survived the freezing process and were classified as intact. The survival rate in this study was 85.4 %, though if only one intact pronuclear oocyte was transferred, no pregnancy could be achieved, whereas if two or three pronuclear oocytes were transferred, seven to ten pregnancies resulted, respectively (23.3 % and 23.8 % pregnancy rates). Eight healthy children have been born to date from four other ongoing pregnancies, one of them is a twin pregnancy.