What is a Blastocyst?
In the human body, an egg cell is fertilised by a spermatozoid soon after its separation from the ovary (ovulation), forming a single-cell embryo (a zygote) containing the genetic material from the spermatozoid and the egg cell. Thereafter, the zygote progressively divides, forming a multi-cell embryo. When the embryo contains 12 to 16 cells, it is termed a morula. Five or six days later, the embryo contains a multitude of cells and a cystic cavity appears at its centre. At this stage, the embryo is called a blastocyst and has undergone the first stage of differentiation by dividing into two distinct tissue types: trophectoderm and inner cellular mass. The trophectoderm will later form the placenta, while the inner cellular mass will form the foetus. In the human body, fertilisation takes place in the fallopian tube, close to the ovary. The developing embryo descends through the tube into the uterine cavity some three or four days after ovulation, when it is at the morula stage. It remains in the uterine cavity about two days, developing into a blastocyst. The blastocyst implants itself into the endometrial lining around the fifth or sixth day after ovulation, enabling it to develop the blood supply (the placenta) that would allow it to grow into a foetus.
What is Blastocyst Transfer?
Blastocyst transfer is a method of cultivating fertilised egg cells, now termed embryos, over 120 hours in specific nutritious environments with a view to optimum selection. The prolonged in vitro cultivation helps select those embryos that have the best biological potential, while stopping the cultivation of a large proportion of embryos with genetic disorders.
The Benefits of Blastocyst Transfer
Transfer takes place close to the natural time when the embryo would enter the uterus: when the uterine lining provides it with a better environment. The laboratory cultivation of embryos for a longer period allows the most vital of embryos – those with the greatest chances of implantation – to be selected. In turn, fewer embryos are returned to the uterus, reducing the risk of multiple pregnancy.
Blastocyst transfer is suitable for younger women who enjoy better opportunities for successful pregnancy following in vitro fertilisation (IVF). Certain families might be recommended blastocyst transfer where a large number of good quality embryos are available but where no implantation has taken place in previous IVF cycles.