Reproductive cryopreservation has recently gained an increasing importance in in vitro fertilization (IVF) programs throughout the world and is probably going to play a significant role over the next few years.

The main vantages of this technique include storage for future use without repeating ovarian stimulation, chance of fertility for neoplastic patients who are going to receive chemotherapy, low risk of multiple pregnancies by reducing the number of fresh embryos transferred, and low risk, without canceling the cycle, of developing ovarian hyperstimulation syndrome (1), which still represents the most serious complication of the superovulation regimes.

Since the first pregnancy and the first birth achieved from human embryo cryopreservation were reported (2, 3), several methods have been developed to make cryopreservation, thawing, and transfer of human embryos more safe, embryo freezing being now routinely used in many IVF programs all over the world.

However, the debate on the safety of cryopreservation is still open, and many authors have expressed their concerns about it, especially after the alarming report in 1995 of morphological and development alteration in mice born from frozen-thawed embryos (4). Moreover, many mutations may be difficult to evaluate since they can have minimal phenotypic effects, with respect viability and macromorphological appearance of offsprings, thus altering behavior and cognitive functions through biochemical and microstructular changes.