Blastocyst Culture & Transfer - Grace Fertility Centre " "

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Blastocyst Culture & Transfer

lastocyst Culture & Transfer

The risk of high order multiple pregnancies is one of the prime concerns with In Vitro Fertilization (IVF). One method to minimize the possibility of such a pregnancy is to transfer fewer embryos. The technique of blastocyst transfer may help to achieve this since a smaller number of more developed embryos are transferred into the uterus, each of which possesses a greater potential to result in a pregnancy.

Frequently Asked Questions

A blastocyst is a highly developed embryo that has divided many times to a point where it is nearly ready to implant onto the walls of the uterus. It has a much greater chance of implanting successfully and resulting in an ongoing pregnancy because it has passed an important test; survival past day three or four. Survival past day three or four is important because during the first few days, the embryo relies on the mother’s egg for all its nutrients. However, in order to survive past this time, the embryo must activate its own genes; not all embryos are successful. Only about one-third of fertilized eggs become blastocysts, yet these embryos are more highly developed, healthier and stronger, and have a higher rate of implantation when compared to day three embryos. Due to the higher probability of survival, we transfer fewer of these embryos back into the uterus depending on your clinical situation and age.

Since it is difficult to predict on day three which embryos are more likely to produce a pregnancy, in women ≥35 years of age, up to three embryos are frequently transferred in hopes that at least one will result in a live birth. With this approach, acceptable pregnancy rates have been achieved although approximately 35% of these are multiple pregnancies, with a possibility of triplets in 7-8%. Multiple pregnancies are associated with considerable medical risks to the mother and infants, as well as financial and emotional considerations. With blastocyst transfer, however, usually a maximum of two embryos are transferred, practically eliminating the possibility of triplets or greater.

In a typical non-blastocyst IVF cycle, a woman’s eggs are retrieved and fertilized. If all goes well, the embryos are transferred into the uterus three days later. In fact, traditional IVF has always transferred on day three because previous laboratory culture media (the solutions in which the embryo survives outside the uterus) could only sustain an embryo’s growth for three days. We now have the ability to develop an embryo to the blastocyst (day five or six) stage. This has now been made possible by the advanced culture systems and improved technology to support blastocyst culture.

It is not possible to predict which day three embryos will develop into a blastocyst but embryos that develop to blastocyst have a higher chance of leading to pregnancy. In general, patients who develop a larger number of eggs and embryos benefit most from blastocyst transfer. A significant correlation (or relationship) has been reported between the number of eggs and the number of blastocysts developed, as well as the number of day three embryos and the number of blastocysts developed. Other candidates for blastocyst transfer include those who would not consider a multifetal pregnancy reduction procedure or those in whom delivering multiple pregnancies would be of particular concern. These patients should strongly consider elective single blastocyst transfer. Blastocyst transfer is probably not beneficial for patients who develop few eggs or few embryos.

Given that only 30% of fertilized eggs develop to the blastocyst stage, it is possible to have no embryos survive to day five to transfer. This is why we generally reserve offering blastocyst transfer to patients with many eggs and to those patients who are anticipated to have several good quality embryos on the traditional day three of transfer. The looming question then becomes: “Would the embryos that did not survive to become blastocysts have implanted if transferred at day three?” Unfortunately, we simply do not have enough clinical data at this time to answer that question. In our opinion, pregnancy would have been unlikely in that situation. But since that outcome is not a certainty, traditional day three transfers are still reasonable for patients with few quality embryos on day three.