Some assisted reproductive techniques, such as in vitro fertilisation (IVF) or ICSI, perform egg fertilisation outside the woman’s body. For this reason, embryo culture is necessary up to the day in which the embryo transfer is performed.
Blastocyst is the stage in which embryo implantation within the uterus occurs naturally. To reach this stage, the embryo is cultured up to day 5-6 by means of a sequential culture system.
Embryos can be classified in 4 categories –from A to D– ranging from best quality to least developed embryos. This classification is mainly visual and rather subjective, but there are also several studies to identify their metabolic activity.
A new study proposes the transfer of the embryos 5 days after the embryo culture, instead of 3 days after. According to this study, it may increase the pregnancy rate and, conversely, decrease the rate of multiple births.