A blastocyst transfer is an embryo transfer which involves transferring one or more embryos that are at a very advanced stage of development, the so-called blastocyst stage. This is usually done on the fifth day after follicular aspiration.
After the doctor has removed the eggs from an ovary (follicular aspiration), they are fertilised in the laboratory. This is done either by normal in vitro fertilisation (IVF) or by means of intracytoplasmic sperm injection (ICSI).
Immediately after fertilisation, an egg starts to divide and develop into an embryo. The stages of development are as follows:
• the pronuclear stage on the first day (fertilised egg)
• the two to four-cell stage on the second day
• the eight-cell stage on the third day
• the morula stage on the fourth day and
• the blastocyst stage on the fifth day
The doctor usually inserts one or more embryos in the woman’s uterus two to three days after egg retrieval. This process is referred to as embryo transfer.
The embryos can also develop in an incubator up to the fifth day, i.e. the blastocyst stage, thanks to improved cell culture media (blastocyst culture). If the doctor transfers such developed embryos into the woman’s uterus, this is referred to as blastocyst transfer.