In Vitro Fertilization Picture of a Morula Stage Embryo - Day 4 Human IVF Embryo
A morula contains about 10 - 30 cells
The morula stage is the final stage prior to formation of a fluid filled cavity called the blastocoel cavity
Once the cavitation has occurred, we can see the fluid in the cavity between the cells and we call the embryo an early blastocyst
Although morula stage embryos are usually seen on day 4 and blastocysts are usually seen on day 5, sometimes we have only morulas on day 5
In that case, we do not know if the embryos are slower than average because they are weaker, or because they are healthy but just developing slower than average
Transferring morulas on day 5 results in a reasonable pregnancy rate, although it is not as high as the pregnancy rate with blastocyst transfer on day 5
Embryo arrest at the morula stage is not uncommon, which is one reason that transfer at the blastocyst stage can be a beneficial IVF treatment strategy.
