The pre-fetus stage is the period of development before a fetus is formed. This stage is known as the EMBRYO and is typically six letters long. During this stage, the fertilized egg divides and grows into a blastocyst, which is a hollow ball of cells. The blastocyst then implants itself in the uterus and begins to develop into an EMBRYO. The EMBRYO continues to grow and develop until it is ready to become a fetus.