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Blastocyst Transfer

Embryos formed as a result of fertilization are cultured in the laboratory for 5 days. In this time, the cells of the embryo rapidly divide and on day 5 it is referred to as a Blastocyst. Transferring a 5-day-old embryo or Blastocyst into a woman's uterus may improve the chances of implantation and in turn, a successful pregnancy. It also reduces the risk of multiple pregnancies, which is a problem with Assisted Reproductive Techniques (ART) and which pose medical risks for both the mother and the infant along with financial and emotional considerations.

Advantages of blastocyst transfer for IVF

  • Embryo implantation process begins about 3 days later - after blastocyst formation and hatching out of the embryonic shell have occurred.
  • Therefore, if in vitro culture conditions are maximized so healthy blastocysts form at a high rate, then day 5 blastocyst embryo transfer can be done.
  • The uterine lining on day 5 should be receptive to the arriving embryo - this a more "natural" time for the embryos to be in the uterus. It is the same timing as with a natural pregnancy.

Many 2 or 3-day-old embryos do not have the capacity to become high quality blastocysts and make a viable pregnancy. However, on day two or three of culture we don't have methods to determine which embryos will be viable long-term, and which will soon arrest their development.

By culturing embryos to day 5 we will find that some of them have not become blastocysts - allowing us an opportunity to choose the most competent embryos for transfer.

We can then transfer fewer embryos and still obtain high pregnancy success rates - with very little risk for having high order (triplets or higher) multiple pregnancies.