Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: After implantation occurs, the blastocyst is called an embryo . The embryonic stage lasts through the eighth week following fertilization. During this time, the embryo grows in size and becomes more complex. It develops specialized cells and tissues and starts to form most organs. For an interactive animation of embryonic development, go to this link: http://health. howstuffworks. com/adam-200129. htm . Answer: an embryo
What is the blastocyst called after implantation?