What term is used to describe a developing embryo starting at 8 weeks of gestational age?

At 8 weeks of gestational age, the developing embryo transitions to the fetal stage, and this stage is referred to as a fetus. The term "fetus" is used from the end of the embryonic period, which concludes at approximately 8 weeks, through to birth. This change in terminology reflects significant developmental milestones, as this is when the major organs and structures have begun to form, and the developing organism is taking on more distinctly human characteristics.

During the previous stage, termed the embryonic stage, from conception until 8 weeks, the focus is on the formation of critical systems and organs. Thus, at 8 weeks, those structures are sufficiently developed to warrant the designation of fetus, indicating a new phase in growth and development. The other terms refer to different stages: “embryo” describes the organism up to 8 weeks, “zygote” refers to the fertilized egg immediately after conception, and “neonate” describes a newborn infant typically within the first 28 days after birth.