Embryogenesis

Definition - What does Embryogenesis mean?

Embryogenesis refers to the complex process of an embryo's development. This occurs during the first 8 weeks after fertilization. Embryos created through in vitro fertilization (IVF) are carefully monitored by an embryologist throughout embryogenesis to assess their quality. The best embryos will be used for transfer or frozen for later use because they are most likely to produce a successful pregnancy.

FertilitySmarts explains Embryogenesis

In the first 8 weeks after fertilization, the embryo goes from a single celled organism to a multi-celled organism with the foundations for all the different systems of the human body. The steps in embryogenesis are:

  1. Zygote - The single cell formed by the fertilization of an egg by a sperm cell.
  2. Cleavage - The rapid cell division that occurs in the first 12-24 hours after fertilization.
  3. Morula - A mass of cells that is formed by day 4 after fertilization.
  4. Blastulation - The formation of a hollow ball within the pre-embryo. It is now called a blastocyst. Implantation occurs at this stage.
  5. Differentiation - Cells begin to differentiate and form cavities.
  6. Gastrulation - The formation of three germ layers (ectoderm, mesoderm, endoderm). The embryo is now called a gastrula.
  7. Neurulation - The beginning of the formation of the neural system.
  8. Organogenesis - The development of organs starting with the heart.

Embryos are typically transferred or frozen between 3-5 days after fertilization. They are monitored as they undergo embryogenesis prior to freezing or transfer. Embryos with abnormalities, such as excessive fragmentation or a stop in cell division, will be given a poorer grade than those without such abnormalities. The embryos with the best grades will be selected for transfer or freezing because they are the most likely to produce a successful pregnancy and a healthy child.

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