This technique involves culture of embryos to day 5 in the incubators, using sequential media, to provide the required nutrients for in vitro growth. 

The purpose of culturing is to witness the possible in utero events in the lab and ensure that the embryos are capable of further growth once transferred within the uterine cavity. 

It also helps filter out those embryos which may be genetically incompetent to grow in utero. However it cannot be universally applied as not all embryos thus grown reach blastocyst stage and they also have a high potential to get arrested. 

The lab must have an existing good implantation rate to be able to get success out of this procedure. The media and culture conditions must also be optimal. 

Some clinical studies have experienced blastocyst rates of 40-65 % and an implantation rate of about the same. Another advantage is that multiple pregnancies can be avoided by transferring a single blastocyst. 

However in our lab we do more of sequential transfers (day2 and day 5) in order to avoid denial of an embryo transfer relying only on blastocysts. 

This procedure also has its indications and with newer media emerging it may prove to be more effective in the coming years.