A fertilised egg becomes an embryo. The development stage of all embryos is assessed in order to check embryo quality and determine which the best embryos are for the transfer.
Two days after follicular puncture or egg retrieval and oocyte insemination, embryos would have shared the genetic information from the male and the female (pronuclei) and their cleavage pattern would be in the 2-4 cell or blastomeres stage.
At this stage, the embryo is referred to as “zygote”. Once it is at the 4-cell stage, it will contain its own genes.
Six days after fertilisation, hatching occurs. Hatching is the process in which the inner cell mass (ICM) breaks through the membrane protecting it in order to become attached to the endometrium in the woman’s uterine cavity.
Seven days after fertilisation, implantation in the maternal uterus occurs because of the interaction between the IMC and the endometrium.
Embryo culture is conducted up to the second or the third day after follicular puncture or the fifth day after the puncture. It is determined on the basis of the type of infertility problem (e.g. the need to perform a PGD), the number of oocytes, embryo development in previous in vitro fertilisation cycles, etc.