Fertilization and Embryo Development of Fresh and Cryopreserved Sibling Oocytes

Background: Oocyte cryopreservation is potentially the best way to preserve female fertility for unmarried women or young girls at risk of losing ovarian function. The aim of this study was to compare fertilization and embryo development in frozen-thawed oocytes to their fresh siblings in women undergoing in vitro fertilization (IVF) and embryo transfer (ET). Materials and Methods: Eleven infertile women undergoing infertility treatment, between the ages of 24 to 37 years (mean +/- SD = 31.6 +/- 3.5), were included in this study. Mature oocytes from each patient were randomized into cryopreserved and fresh groups prior to intracytoplasmic sperm injection (ICSI). One hundred and thirty nine oocytes were retrieved, of which 105 were at metaphase II (MII). Forty-five fresh MII oocytes were kept in culture whereas their sibling 60 MII oocytes were cryopreserved using a slow cooling protocol. The frozen oocytes remained in LN2 for 2 hours before thawing. ICSI was performed 1-2 hours after thawing for frozen oocytes and 4-5 hours after retrieval for fresh oocytes. Fertilization and embryo development were compared. Results: Following thawing, 31 oocytes (51.6%) survived and 22 fertilized (79%) while 32 fresh oocytes fertilized upon ICSI (71%). The mean +/- SE scores for embryos developing from frozen-thawed oocytes were significantly lower at 48 and 72 hours post-ICSI than for embryos resulting from fresh oocytes (p<0.05). Conclusion: Our data demonstrated that oocyte freezing resulted in acceptable survival rates following cryopreservation, and similar fertilization rates following ICSI as compared to the fresh sibling oocytes. However the number of blastomeres and the embryo quality on day three was superior in embryos from fresh oocytes when compared to the frozen oocytes.