The success rate for blastocyst is always higher than day 3 embryo so I'm not sure how they are going to do the control trial. My understanding is that clinics grow embryo to day 5 will use a different media than day 3. That's why low cost clinics only grow to day 3. It is the technology (different incubator?) and extra stuff that go with it costs money for further culturing. From the sound of it, it is a new type of media for culturing the embies to day 5. If you havent heard of embryo glue, it is another one that i don't know how they can easily test the success rate (just thinking about a natural conception doesn't require it).