Following a number of physical phenomena, there is a build up of liquid in the cavity which ends up forming what we know as the blastocoel. A progressive accumulation of liquid leads to an increase in the size of the blastocyst and this increases the pressure both in the trophectoderm and in the zona pellucida (the layer surrounding the blastocyst which protects it from the exterior environment). The collapse phenomenon is caused by liquid exiting the blastocoel. The embryo needs to exit the zona pellucida in order to implant and we believe that the expansion and collapse phenomena are linked to embryo eclosion.
A number of studies have attempted to link the number of collapses to the embryo’s ability to implant. However, no conclusions have been reached so far. Additional studies are necessary in order to be able to fully confirm this connection. It has been recorded that collapse is a process which is inherent to development and it would appear to be associated with correct progress of the embryo.