If you are opting for a Blastocyst culture in your IVF cycle a day 5 embryo ( blastocyst ) will be transferred in your uterus either as a part of fresh or Frozen. A Blastocyst transfer is preferred in order to allow selection of the best quality embryos for transfer. Embryo quality is important for fertility outcome. With blastocyst transfer, we can transfer fewer embryos – reducing multiple pregnancy risks, and maintain high IVF success rates. A Blastocyst is a stage of embryo five days after fertilization, it has two distinct parts - the outer layer of surface cells called the Trophoectoderm and a more central group of cells called the Inner Cell mass.
Under standard IVF culture conditions, only about 25 to 60% of human embryos progress to the blastocyst stage after 5 days of culture, this could be due to sub optimal condition in lab or due to inherent weakness of embryos.
Blastocyst culture allows selection of better more competent embryos for transfer thus offering better results. Also they allow fewer embryos to be transferred so decreasing the risk of multiple pregnancies . Also a Blastocyst can be easily biopsied for Pre implantation Genetic Testing.
If the IVF clinic is proficient at Blastocyst culture and has excellent quality control in the laboratory, there is potentially no disadvantage to Day 5 Blastocyst transfer. but in few patients especially in those with low ovarian reserve there are chances of cycle cancellation as there is a possibility that none of embryos reach that particular stage.