IVF PRIMER

Three days after insemination or ICSI, normally developing embryos contain about 8 cells.

Five days after insemination or ICSI, normally embryos have developed to the blastocyst stage, which is typified by an embryo that now has 80 or more cells, an inner fluid-filled cavity, and a small cluster of cells called the inner cell mass.

It is important to note that since many eggs and embryos are abnormal, it is expected that not all eggs will fertilize and not all embryos will divide at a normal rate.  The chance that a developing embryo will produce a pregnancy is related to whether its development in the lab is normal, but this correlation is not perfect.   This means that not all embryos developing at the normal rate are in fact also genetically normal, and not all poorly developing embryos are genetically abnormal.  Nonetheless, their visual appearance is the most common and useful guide in the selection of the best embryo(s) for transfer.

Eight-cell embryo 3 days after retrieval

Blastocyst 5 days after retrieval