From the early blastocyst stage and onwards, a typical phenomena visualized in time-lapse is a slow expansion of the blastocyst, followed by a rapid contraction which is repeated 4-5 times. In our opinion this is a healthy sign of importance for the hatching process. In the contracted stage the morphology is very difficult to evaluate and a new evaluation in the microscope is necessary a couple of hours later.
The sequence also demonstrates the forceful intracellular movements, which reforms the shape of the blastocysts shortly before hatching. Even when the hatching procedure has started the typical pattern with contractions followed by expansions continues. The compact cell cluster, the inner cell mass, is surrounded by trophectoderm cells.
Following hatching the blastocyst is ready for apposition and attachment to the endometrium.