Blastocyst culture has increased immensely in the last decade and is now routine practice; this has resulted in some benefits such as increased pregnancy rate per embryo transferred compared to cleavage stage transfer and a decrease in multiple pregnancy rates without a decrease in pregnancy rates overall when a single blastocyst is transferred. Potential disadvantages of blastocyst transfer include increased cycle cancellation rates, an altered sex ratio (favouring males), a reduction in embryo cryopreservation rates and an increase in preterm birth rates. Crucially, there is no robust evidence that blastocyst culture and transfer results in equal cumulative pregnancy rates compared to cleavage stage transfer, meaning that blastocyst transfer may be detrimental in some cases. Ultimately there is no robust evidence that all embryos that fail to blastulate in-vitro would do so in-vivo, and so centres should continue to utilise treatment algorithms that include both blastocyst and cleavage stage transfer options.