Blastocyst culture is a process in which embryos are cultured in the laboratory for 5 or 6 days, until they reach the blastocyst stage. At this stage, the embryo has a more complex structure consisting of an inner cell mass, which will develop into the foetus, and an outer layer of cells called the trophectoderm, which contributes to the formation of the placenta.
Reaching this stage before transfer allows embryologists to obtain additional information about embryo development and can help support embryo selection in appropriate cases.
Once transferred to the uterus, the blastocyst generally takes 1 to 3 days to implant in the uterine wall. During this process, the blastocyst attaches to the endometrium (the uterine lining), starting pregnancy. During this time, the body must be prepared to receive the embryo, often with the help of hormonal medications that create a favorable environment for implantation.
Blastocyst culture is carried out in several phases:
The patient's ovaries are stimulated to produce multiple eggs, which are then collected through an egg retrieval procedure.
The retrieved eggs are fertilised with sperm in the laboratory, either through IVF (in vitro fertilisation) or ICSI (intracytoplasmic sperm injection).
The embryos are placed in a special culture medium and observed over several days until they reach the blastocyst stage.
Once this stage is reached, blastocysts are assessed according to their development and quality to support embryo selection for transfer.
The selected embryo is transferred to the woman's uterus.
After transfer, the blastocyst may implant in the endometrium, beginning the implantation process.
The decision to transfer embryos at the blastocyst stage depends on various factors. Fertility specialists may consider transfer at this stage in cases such as the following:
Transfer at the blastocyst stage can offer several advantages in appropriate cases:
There are different types of embryo cultures depending on the case:
Embryos are cultured for 3 days before transfer. Whether a day 3 or blastocyst-stage transfer is considered depends on the individual treatment and embryo development.
This is the most common when there are enough good-quality embryos, allowing the embryos to reach an advanced stage before being transferred.
Culture with preimplantation genetic testing (PGT): At the blastocyst stage, an embryo biopsy may be performed for genetic analysis before an embryo is selected for transfer.
Time-lapse technology allows embryo development to be monitored at regular intervals without removing the embryos from the incubator for observation.
Blastocyst transfer can allow further assessment of embryo development before transfer and may be appropriate for selected patients. However, treatment success depends on multiple factors, including maternal age, embryo quality, the number of embryos available, the type of treatment and individual clinical circumstances.