embryo medical definition

1. An organism in its early stages of development, especially before it has reached a distinctively recognizable form.
2. An organism at any time before full development, birth, or hatching.
3. The fertilized egg of a vertebrate animal following cleavage.
4. In humans, the prefetal product of conception from implantation through the eighth week of development.

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embryo

Clockwise from top left: human embryo at five, seven, and eight weeks of development