Embryos produced in IVF may be capable of continued normal development leading to a successful pregnancy. One of AART’s challenges is choosing the embryos most likely to result in a successful pregnancy. In vitro culture has improved enabling culturing of embryos for up to five days. By this time the embryos have reached a stage of development called the blastocyst. Extended culture time enables AART to select those embryos with the highest probability of producing a pregnancy.