What causes can prevent an embryo from reaching blastocyst?

Embryos with a defective genetic endowment or any other problem (poor oocyte and/or seminal quality), will not be able to activate their genome and will not manage to reorganize to form a blastocyst. 

It is important to make an accurate assessment of the causes that prevent the development of the embryo to the blastocyst stage in order to correct it and improve pregnancy rates in the future.