Abnormal embryonic development Abnormal preimplantation embryonic development 2020-11-29T17:49:55Z An anomaly in the development of the embryo in a stage prior to implantation. Human embryo development begins in relative transcriptional silence with an oocyte to embryo transition that lasts for about 3 days and encompasses fusion of the egg and sperm, migration and fusion of the germ cell pronuclei, genetic and epigenetic reprogramming. The embryo subsequently undergoes compaction to form a morula that marks the first morphological indication of a break in radial symmetry. Subsequent cell divisions lead to the development of a blastocyst that comprises a fluid-filled blastocyst cavity and an inner cell mass, surrounded by trophectoderm cells. Implantation, which in humans occurs at approximately day 7 of development, is required for further development of the embryo proper.