"A blastocyst embryo has reached a stage in development that requires activation of the embryo's own genes, called genomic activation. Genes are chemical codes that make us unique. When a sperm and egg fertilize the resulting baby is a mixture of the genes from the mother and father. This mixture creates a child who is unique and different from mother, father, or siblings. During early growth of the embryo, all of the energy and chemicals required for cell division come from the mother's egg. In order to continue to develop past the third or fourth day of life, the embryo must activate its own genes to produce energy for further cell division and differentiation. Sounds simple! Although this biological process is critical, it does not occur as easily as we might hope. Approximately one third of embryos are capable of successfully activating their genes and growing to the blastocyst stage. If an embryo reaches the blastocyst stage, nature is telling us that it is a healthier embryo and it has a better chance of implanting successfully and resulting in a normal, healthy, baby."
North Hudson IVF of New Jersey has even better information:
"When embryos are cultured to the blastocyst stage in the IVF laboratory, it is common to see about half of the embryos stop growing by the end of the third day. This rate of attrition is normal and is a result of the poor developmental potential of some of the embryos. Once an egg is fertilized, no genetic instructions are required for the embryo to reach the four-cell stage of development. However, on the third day, when the embryo is between the 4- and 8-cell stage of development, new genetic instructions are required for continued growth. About half the time, the genetic information required for growth beyond the 8-cell stage is conflicting, garbled or missing and the embryo simply stops growing. At present, it is beyond the IVF laboratory's capability to correct or improve the genetic potential of a developing embryo. It is important to also note that since the environment within the lab or the uterus cannot influence the genetic make up of the embryo, the same attrition is observed when the embryos are transferred to the uterus on Day 3. That is, transferring genetically compromised embryos to the uterus on Day 3 does not improve their chances of continued development."
I guess that's why my embryos never made it past four cells, except for the few that kept going. Even those embryos risk arresting because they haven't made it to blast yet. I guess I'll now in about two weeks, but at least I have some answers instead of none.