Comparison of embryo development of ICSI and IVF derived embryos from modified natural cycles according to time-lapse technology

Background: to compare the effect of intracytoplasmic sperm injection (ICSI) and conventional fertilization (IVF) on the development of embryos derived from modified natural cycles, in order to find the most effective fertilization method. Methods: Seventy-two embryos were evaluated, of which 43 resulted from intracytoplasmic sperm injection (ICSI) and 29 from conventional fertilization (IVF). The evaluation was performed according to the KIDScore Day 5 algorithm, but also according to the Gardner and Schoolcraft evaluation system. The quality of each embryo was evaluated and categorized according to their quality on the 5th day of their development, the presence of multiple nuclei at the 2 and 4 cell stage (MN2, MN4 respectively), the direct cleavage of blastomeres (DC) and the reverse cleavage of blastomeres (RC). Additionally the time points of each cellular event was recorded. Results: The fertilization method is independent of the qualitative classification of embryos, the appearance of multiple nuclei, the direct cleavage and the reverse cleavage of blastomeres. The time points of cellular events were similar between the two fertilization methods. Conclusions: No significant difference was observed in the development of ICSI and IVF derived embryos from modified natural cycles. Therefore, neither of the two fertilization methods is considered more appropriate for the embryonic development in modified natural cycles. It is suggested to evaluate both the medical history and the gametes quality of the couple in order to choose the appropriate fertilization method. It is also recommended to use both methods of embryos evaluation in combination.