The embryo stage is defined as occurring during which weeks?

• A. 1-2 weeks
• B. 3-8 weeks
• C. 9-12 weeks
• D. 13-16 weeks

Answer: (B)

The main idea is that the period of organ formation, when the basic body plan is established, happens during the embryonic stage. This spans roughly from week 3 through week 8 of development. During this window, essential processes—like neural tube formation, heart development and initial beating, limb buds forming, and the beginnings of most organ systems—occur. By the end of week 8, the groundwork for all major organs is in place, though they continue to mature later. Weeks 1–2 are the pre-embryonic phase, focused on fertilization and implantation, while weeks 9 onward are the fetal period, characterized more by growth and refinement than primary organ formation. So the embryo stage is during weeks 3–8.