Cleavage stage versus blastocyst stage embryo transfer in assisted conception.

Despite numerous advances in the field of in vitro fertilisation (IVF), many of the widely applied embryo culture techniques and resulting implantation rates have remained relatively unchanged since the first treatment was performed in the mid 1970's. Recent advances in the understanding of nutrient requirements of embryos, have led to a renaissance of extending their culture from the standard procedure of 2-3 days (early cleavage embryo transfer) to 5-6 days (blastocyst culture). The rationale for blastocyst culture is to improve the synchronicity of uterine and embryonic development and provide a mechanism for self-selection of viable embryos. Numerous reports on the clinical benefits of blastocyst culture have led to the worldwide introduction of this technique, despite a deficiency of conclusive evidence to do so.