Blastocyst Culture, or extended culture, allows IVF-derived embryos to reach a more advanced stage of development in the laboratory prior to their transfer into the womb; this process facilitates selection of the best quality embryos for transfer to the uterus of the mother.

Most fertilized eggs can develop relatively well up until three days in culture; at this point, normally developing embryos "turn on" their newly arranged genomic machinery in order to use more complex nutrients and continue development. Only about 20 to 40% of embryos that are growing on day 3 continue on and become blastocysts; many embryos fail to activate their genome and therefore stop developing in culture.

The term blastocyst is used to name the stage of development of an embryo by day 5. Blastocysts form between Days 5 and 7 in culture and are composed of two distinct cell types and a central cavity filled with fluid (blastocoel cavity). The surface cells that surround the cavity (just under the outer shell) are called the "trophectoderm" and will later develop into the placenta. The more centrally located group of cells are called the "inner cell mass" and will become the fetus.

The embryo in the picture is a high quality day 5 blastocyst which resulted in pregnancy and delivery of a healthy baby girl. Blastocyst culture is beneficial in reducing multiple pregnancies as these more advanced embryos have higher implantation potential than earlier stages, therefore, allowing for the transfer of lower numbers to the womb while keeping pregnancy rates high.