A blastocyst is a cell mass that forms early in mammalian embryo development, containing an inner cell mass that becomes the fetus and a trophoblast that becomes the placenta. Blastocyst transfer in IVF is preferred as it is more likely to result in pregnancy and reduces the risk of multiple pregnancies. Blastocysts are also important in embryonic stem cell research.
A blastocyst is a cell mass that forms early in the developmental process of the mammalian embryo. In humans, this stage of embryogenesis occurs five days after fertilization when there are fewer than 100 cells in the mass. At this stage of development, the embryo has not yet implanted itself in the uterus.
The fertilized eggs are known as zygotes. Once fertilized, the egg undergoes a rapid series of cell divisions, followed by cell differentiation.
Inside the blastocyst, there are two types of cells. Inside is the inner cell mass, part of which will begin dividing at a very rapid rate and become the developing fetus. It is surrounded by a fluid-filled cavity called a blastocoel. Surrounding this is a single layer of cells called the trophoblast, which will join the endometrial cells of the uterus to become the placenta.
Many people undergoing IVF prefer blastocyst transfer as an alternative to three-day embryo transfer. Transferring blastocysts, which are slightly older, may be a more effective option because they tend to be more stable than three-day-old embryos and are more likely to result in pregnancy. This is because about 50% of embryos do not reach the fifth day of development; by using these embryos, therefore, there is a greater chance that they will be viable after transfer.
Another benefit of using these older embryos for implantation is that since there is a higher chance of viability, there is no need to implant as many. Many people prefer this option because there is a much lower chance of multiple pregnancies, which can be dangerous for the pregnant woman and developing babies, with an increased risk of underweight babies, miscarriage and stillbirth.
Blastocysts are important in a field of scientific research called embryonic stem cell research. Embryonic stem cells are thought to have special properties that other types of stem cells do not have, perhaps due to the fact that, in embryonic cells, gene expression has just begun. The embryos used in this type of research are obtained from IVF clinics with the express permission of the biological parents. Generally, people allow their embryos to be used this way if they are no longer needed for implantation and if they are comfortable with using them in research.
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