Blastocyst culture: myth or magic?

The development of sequential serum-free culture medium has led to a reported increase in implantation rate after transfer of embryos on days 5-6 (approximately 40%) compared with those achieved after transfer on days 2-3 (approximately 20%). However, there are numerous uncertainties surrounding extended culture that need to be considered. This article examines some of the problems and questions considered in relation to the following areas: the developmental capacity of the embryo in vitro; the uterine environment after embryo transfer; the clinical indications surrounding blastocyst transfer including a reduction in multiple pregnancy rate and relevance in preimplantation genetic diagnosis (PGD); and the introduction of blastocyst culture into the embryology laboratory.