Blastocyst Transfer and Reduced Multiple Births
In an IVF cycle, embryos are cultured until mature and ready for transfer, which is usually from three to six days. As the embryos develop, they pass through several developmental stages including blastocyst formation. (We typically refer to day 5 embryos as blastocysts, however, embryos may form blastocysts before or after 5 days.)
A blastocyst is a developing embryo that has differentiated (or separated) into two distinct cells types. The surface cells are termed the trophectoderm and will eventually become the placenta and the inner cell mass will become the fetus. A healthy blastocyst should hatch from its shell (zona pellucida) by the end of six days or earlier and begin to implant within the lining of the uterus.
Blastocysts are typically “stronger” than day 3 embryos. In Darwinian terms, only the strongest, and most fit, embryos will survive the additional two days in culture. Blastocysts have a higher IVF implantation rate and are more likely to survive than day 3 embryos. Because of this increased viability, fewer blastocysts need to be transferred in the IVF cycle thus dramatically lowering the rate of high order (>2) multiple births.
However, even with the advantages of increased viability and lower multiple birth rates, blastocyst transfer is not for every couple (cycle). The longer the embryos are cultured the fewer the embryos that will remain viable for transfer. For example, there are usually more embryos on day 1 than on day 3 or day 5 as some embryos stop growing or their growth slows during the culturing process.
There must be enough viable embryos on day 3 to “risk” culturing to day 5. For example, if only two embryos are present on day 3, one or both, could stop growing by extending culture to 5 or 6 days, which would result in the loss of the cycle. On the other hand, if 6 good embryos are available on day 3, the chances are very good that 2 or more will survive to day 5 making blastocyst transfer feasible. Whether or not the couple plans to cryopreserve some of their embryos will also influence the decision on whether to extend the culture.
Our physicians discuss the appropriateness of blastocyst transfer with each couple.
Assisted hatching is a procedure designed to improve embryonic implantation rates. It is performed in conjunction with an in vitro fertilization cycle (IVF) , where an embryo is created as a result of FSH stimulation, egg retrieval, and fertilization.
AH requires that a small hole be etched in the embryonic membrane or outer shell of the embryo, known as the zona pellucida. It is theorized that this hole makes it easier for the embryo to “hatch” out of its protective membrane and embed into the endometrial lining.
The hole can be produced chemically using Acid Tyrode’s solution, mechanically, or with a laser. Creating an opening in the membrane does not usually affect the embryos survivability. Assisted hatching is most often considered in couples who fail repeated IVF attempts, older women (over the age of 36), when poor quality embryos are suspected or when the zona pellucida is thicker than normal.
*Be sure and read the IVF overview as it provides information necessary to understand blastocyst transfer and assisted hatching.
ART Links
|
