Oocyte freezing methodologies at an italian assisted reproduction centre

Abstract

OBJECTIVE: Due to the introduction in Italy of Law 40/2004, which forbids embryo freezing, interest in oocyte cryopreservation techniques has notably increased. Oocyte cryopreservation, besides being a methodology used to preserve female fertility represents the only alternative to use supernumerary oocytes. The study compares two different slow freezing protocols by considering survival, fertilization, cleavage and pregnancy rates. DESIGN: Cryopreserved oocytes evaluation. MATERIALS AND METHODS: Oocytes were frozen using two different slow cooling protocols, which make use of PROH (1.5M) and different sucrose concentrations (0.2M and 0.3M) as cryoprotectants. Oocytes of 151 patients have been cryopreserved; 143 of these patients froze the supernumerary oocytes, 4 due to oncological pathology and 4 due to the risk of ovarian hyperstimulation syndrome. Two protocols were tested sequentially and performed by the same operators. Sucrose 0.3M Protocol (Group 1): January 2003 - December 2006, Sucrose 0.2M Protocol (Group 2): since January 2007 and still in progress. No restriction in the selection of the patients. The rapid thawing protocol was the same for all cohorts of oocytes, and cryoprotectants were removed by step-wise dilutions. RESULTS: In Group 1, after 126 freezing cycles, 80 thawing cycles were performed and 459 oocytes were thawed. The survival rate was 71.9%. Fertilization and cleavage rates were 46.2% and 65.2% respectively. On the whole, 90 embryos were transferred and 9 pregnancies were achieved, with a pregnancy rate per thawing cycle of 11.2%, as well as an implantation rate of 6.6%. Three of them came to the end, while 5 ended up with a miscarriage and one is still ongoing. In Group 2, since January 2007, 53 freezing cycles and 17 thawing cycles have been carried out, for a total of 85 thawed oocytes. The survival rate was 64.7%, while fertilization and cleavage rates were 60.4% and 81.2% respectively. Altogether, 26 embryos have been transferred, and 5 pregnancies have been achieved, with a pregnancy rate per thawing cycle of 29.4%, as well as an implantation rate of 19.2%. Three of five pregnancies ended up with a miscarriage, while two of them are still ongoing. CONCLUSIONS: Although the data for the Sucrose 0.2M and 1.5M PROH protocol are still limited due to the poor number of total performed cycles, the study highlights a trend of improvement in oocyte fertilization, cleavage and implantation rates even if decreasing survival rate.