Which statement accurately defines embryo and fetus?

• A. Embryo is 0-2 weeks; fetus is 2-8 weeks
• B. Embryo is 0-4 weeks; fetus is 4-8 weeks
• C. Embryo is 0-8 weeks; fetus is 8 weeks to birth
• D. Embryo is 2-6 weeks; fetus is 6-40 weeks

Answer: (C)

Developmental stage distinctions hinge on what’s happening in the baby’s body. In the first eight weeks after fertilization, the embryonic period unfolds, and major organ systems are formed. By the end of this window, the basic body plan is established, and the developing baby is then described as a fetus, a stage that lasts from about eight weeks until birth and is focused on growth and maturation of those structures. So defining embryo as 0–8 weeks and fetus as 8 weeks to birth matches the point at which organ formation is complete and growth takes over. Keep in mind some curricula use gestational age (from the last menstrual period), which can shift the numeric boundaries a bit, but the idea remains the same: organogenesis during the embryo stage, growth and refinement during the fetal stage.