Virtual Embryology Tour: Embryo Development

One of the advantages to in-vitro fertilization is the ability to monitor embryo development prior to embryo transfer. This allows us to identify those embryos that have the highest pregnancy potential. There are many factors that we use to monitor embryo development including their cell number, growth rate, morphological appearance and development to the blastocyst stage. None of these factors are 100% predictive of pregnancy, however, we can maximize chances of pregnancy by considering all these factors together.

The eight-cell embryo (top picture) is at day 3 of development and is considered a good quality embryo based upon cell count, morphology, and developmental rate. The blastocyst stage embryo (bottom picture) is at day 5 of development and contains a cystic cavity with a distinct inner cell mass (which is the embryo proper) and trophectoderm which will form the placenta.

Embryos are transferred on either day 3 or day 5 of development depending primarily on the number and quality of embryos on day 3. The culture of embryos to the blastocyst stage can provide additional information to help the physician and embryologist select the best embryos.