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Blastocyst Transfer

What is a blastocyst ?

A blastocyst is a preimplantation embryo and can be considered as the last stage of embryonic growth, which can be cultured outside the body. After this stage, the embryo requires the uterus to grow into a human being. It has 30-200 cells in it and has two distinct types of cells unlike only one type of cell in early cleavage stage embryos (from 2-32 cell). The two distinct cell types of a blastocyst are- the inner cell mass which, after implantation gets converted into the fetus and, trophoectoderm., which becomes the placenta

Until recently, it was a common practice of almost all IVF centers to transfer embryos at the cleaving pre-embryo stage (usually 4-16 cells). This required culture of the embryos for 2-3 days in the laboratory. Recent development of advanced sequential culture media have allowed embryos to be cultured for 5-6 days so that they can reach to blastocyst stage

What are advantages of blastocyst culture?

Extended embryo culture in IVF theoretically allows the identification of those embryos with the highest developmental competence. It also helps in synchronizing embryonic age with endometrium to facilitate early communication between the two. This technique involves more than a single culture medium in order to accommodate the metabolic needs of the growing embryo. At present, the blastocyst formation rate per fertilized oocyte is in the range of 30-40 %. Other benefits include-

  • It is more physiological
  • It has high implantation rate
  • It gives us an opportunity for a better embryo selection
  • It increases predictive value of pregnancy
  • It reduces multiple pregnancy rates as less number of embryos are transferred.
  • It is more suitable for PGD and cryopreservation

Are there any drawbacks of blastocyst transfer?

  • This is applicable to a group of selected patients with younger age and those with moderate to good response to the stimulation protocols
  • This has more embryo transfer cancellation rate because of 'no blastocyst' situationM
  • This has a higher tendency of giving birth to monozygotic twinning
  • This results in more 'embryo wastage' as less number of embryos reach to blastocysts in vitro
  • There are many groups which have reported similar pregnancy rates with Day 2 -Day 3 embryo transfers, which can avoid unnecessary prolonged in vitro culture of embryos thus keeping laboratory costs at low level

Blastocyst culture is a promising concept but it has to be carefully applied to the existing IVF set up. A sudden changeover to Day 5 transfer may not fulfil the expectations. Like ICSI, its application should be decided on patient-to-patient basis and should not be generalized to all, to avoid disappointments. A more detail information about the outcome of blastocyst transfer from all centers will provide helpful guidelines for the most effective use of this concept.

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