Blastocyst Stage

There is much talk in the world of ART concerning the blastocyst stage of embryonic development. But what exactly is a blastocyst and why is it so important?

In a word, a blastocyst is an embryo that has developed for five to six days following fertilisation. Under natural conditions, it is at this stage of development that an embryo reaches the uterus before attaching to the endometrium a few days later. Up to this time, the embryo (or ‘pre-embryo’) has been travelling down the fallopian tube, changing from a single-celled zygote into a multi-celled organism in preparation for implantation.

In classical IVF, embryos are transferred after only two to three days of culture—before the ideal stage of growth has been reached. However, through a process termed extended culture, we can now achieve the blastocyst stage in the lab over a period of five days. During this time, a kind of natural selection also takes place, in which only high quality embryos tend to survive to day 5.

By using a blastocyst for transfer, we are thus able to reasonably ensure embryo quality and more closely duplicate nature’s timing, both of which can appreciably improve the likelihood of conception for you and your partner.