Updated: Oct 14, 2021


best fertility centre

A blastocyst is an embryo that has developed in the laboratory for five days after insemination. Blastocysts have a large, central, fluid-filled cavity and two distinct cell types.


best fertility centre

‘Blastocyst culture’ refers to culturing or ‘growing’ embryos from the Day 3 stage to Day 5 or Day 6.

By growing embryos for a longer period of time in the lab, we can gain additional information about those embryos. This is particularly helpful when selecting the best embryo for Embryo Transfer.

Not every embryo will reach the blastocyst stage, but those that do have shown they have a greater chance of implanting in the womb.

Until recently, successfully culturing embryos to the blastocyst stage was difficult. Initially, only 17% of embryos reached the blastocyst stage and pregnancy rates using blastocysts were only 10%. Scientific advances have led to the development of culture media that mimic the changing environment of the reproductive tract and meet the unique requirements of the embryo as it travels through the fallopian tubes. Our blastocyst formation rate averages at 65% of embryos to successfully grow to the blastocyst stage in the laboratory environment.


In the IVF laboratory, after the egg retrieval procedure, fertilization is carried out by IVF (In-vitro fertilization) or by ICSI (intracytoplasmic sperm injection) and the resulting embryos are placed in an incubator for further development.

The stages of development are as follows:

  • The day of egg retrieval is considered as Day 0 (IVF or ICSI is done after egg retrieval)

  • The pronuclear stage on day 1 (embryologist checks as to how many eggs have successfully fertilised)

  • The two to four cell stage on Day 2

  • The eight cell stage on day 3

  • The morula stage on day 4

  • The blastocyst stage on day 5 or day 6

The blastocyst contains two different cell types- the inner cell mass which develops into the fetus, and an outer layer of cells called trophectoderm which develops into the placenta.


Blastocyst culture is advised for:

  • For patients with multiple failed IVF: Performing a blastocyst culture on a patient with a history of failed IVF with day 2/3 embryo transfer, can yield more information related to the growth of the embryos and aid in improving pregnancy rate.

  • To eliminate multiple pregnancies: Blastocyst culture allows the possibility of transferring the single best embryo and thereby reducing the chance of multiple pregnancy.


Blastocyst culture requires optimal laboratory conditions. On an average, about 45% of fertilized eggs reach the blastocyst stage.

The appearance of an embryo is not always capable of predicting blastocyst formation or implantation potential. On average, only 15-20% of 2-4 cell embryos transferred to the uterus will implant. Blastocysts, in comparison, have an implantation potential of up to 60% per blastocyst.

The ability to transfer a single blastocyst with a high implantation rate as opposed to Day 2 or Day 3 embryos, will increase the chance of a healthy singleton pregnancy and reduce the incidence of multiple births with the associated risks.

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