Silvia Azaña, an embryologist at inviTRA, explains in this video the stages of embryonic development observed while the embryo is in culture in the IVF laboratory:
Next, we will briefly review the stages that embryologists evaluate to select the embryo that is most likely to implant and therefore to result in a pregnancy.
Day 1. This is the day after the follicular puncture and it is when it is assessed 16 to 18 hours after fertilization whether it has occurred correctly. At this stage, the embryos are called zygot.
Day 2. The embryos have already undergone the first divisions and have two to four cells also known as blastoirs.
Day 3. At this point, the embryos have about six to eight blasts. The embryo is beginning to express its own genes, so its needs are gradually changing.
Day 4. The embryo is in the modulus stage and is compacting.
Days 5 and 6. During these days, the embryo reaches the blastoyst stage. Embryos that reach this stage with good morphological characteristics have a high likelihood of implanting.
However, not all embryos reach day five or six of development. There are several reasons why embryos may stop at any point in their development, but the most common reason is that embryionic development is halted due to some genetic anomaly within it.
