What is the major distinguishing factor that separates embryonic and fetal stage?

The major distinguishing factor that separates the embryonic and fetal stages is the development of distinct organ systems. The embryonic stage, which lasts from fertilization to about eight weeks, is characterized by the formation of basic structures and tissues. In contrast, the fetal stage begins around the ninth week of pregnancy, during which these structures mature and grow, leading to the development of recognizable features and functionalities in preparation for birth.