| Blastocyst |
this is the stage that embryos reach 5-6 days after the eggs are removed and fertilized in a lab. It is an advanced stage of embryo development where the embryo consists of an outer thin layer of cells (which later develops into the placenta) and inner cells (which later develop into the fetus). In a natural pregnancy this would be the same stage as the embryo reaching the uterus. In IVF the eggs are usually implanted 2-3 days after removal. However if eggs are left to the blastocyst stage they divide many more times into many more cells than if left for 2 - 3 days. The chances of selecting good eggs to implant are increased. Blastocyst transfer occurs when embryos at the blastocyst stage are transferred into the uterus. This technique can be incorporated with IVF to increase pregnancy rates and decrease the risk of multiple pregnancies. |