In normal conditions (natural conception), after fertilization, the embryo grows until the blastocyst stage. The blastocyst grows as the cells divide and the cavity expands, where it “hatches” from the zona pellucida to implant into the endometrium. The blastocyst is the highest degree of development that an embryo can reach in vitro.

The factors influencing the development of blastocyst invitro are the age of the woman, the number of oocytes retrieved and the intrinsic and culture conditions. The embryos that develops till blastocyst stage are lesser in number than fertilized ones. This is majorly because of the metabolic block of the embryo invitro during the cleavage stages due to maternal, paternal and embryonic genomes. This metabolic block is overcomed by blastocyst stage embryos, even though the number of embryos available for freezing may be lower but the pregnancy rates following the transfer of a blastocyst is better. In in vitro fertilization (IVF), the blastocyst culture is important to increase the success rate of IVF because of better embryo selection after better genomic activation and endometrial receptivity.