Day 3 Fertilization Results: What is the embryologist looking for?

After your eggs are retrieved as part of an IVF procedure, they are cultured in the lab for up to 7  days. The embryology team will check in on their growth periodically using a microscope. They look for certain signs that tell them how each embryo is developing. This post details what the embryology team is looking for on day 3 of fertilization.

Day 3 embryos are known as cleavage stage embryos. At this stage, the embryos are the same size as the single-celled egg but are starting to divide into separate cells. Usually by day 3 the embryos should have about 6-10 cells and sometimes even a few more.  Embryologists visually grade each embryo based on how many cells there are, how uniform each cell is (symmetry), and the amount of cell fragments that are separating from and surrounding the embryo (fragmentation).

The highest graded embryos have:

• ≥ 10 cells 

• >50% symmetry

• <10% fragmentation

• Mono-nucleated (one nucleus per cell) 

Embryo grading is somewhat subjective because it’s based on what one embryologist sees at one moment in time. Remember that even lower graded embryos can still result in successful pregnancies.