Which stage marks the transition into the embryonic period?

The transition into the embryonic period is marked by the stage from 2 weeks to 8 weeks of gestation. During this time, after conception, the developing organism undergoes significant changes, where it starts as a zygote, then moves to the blastocyst stage, and finally implants into the uterine wall. This period is crucial as the foundations for all major organs and structures are established, which is why it is classified as the embryonic stage. Key developmental processes such as organogenesis occur during these weeks, leading to the formation of vital systems in the body.

The other timeframes provided do not accurately reflect the beginning of the embryonic period. The period from conception to 14 days mainly encompasses the pre-embryonic stage, during which implantation occurs, but significant organ development has not yet begun. The range from 14 days to 12 weeks is primarily considered the fetal period, where the structures formed in the embryonic phase continue to mature and grow. Lastly, the timeframe from 8 to 20 weeks also falls within the fetal period, emphasizing growth rather than the critical development that characterizes the embryonic period.