The blastocyst culture (also called sequential culture) is the development of the embryos in the laboratory to the blastocyst stage. This may happen on the 5th or 6th day of development. From the technical standpoint, embryos can be left in the laboratory until the 5th or 6th day thanks to the development of culture media containing the nutrients the embryo needs in the initial stages. The metabolic needs of the embryo change during these first days of development, therefore, specific culture media are required..

his is why it is called "sequential culture", since the culture media are changed as the embryo develops. The maximum time that embryos can be cultured in the laboratory is 6 days. Most of the embryos reach the blastocyst stage on the 5th day; however, others can reach this stage on the 6th day.

When it has been decided to do a long culture (or sequential), the time of the transfer is when the embryo reaches the blastocyst stage (either the 5th or the 6th day).