Final answer:
During the first trimester, the embryo moves to the uterus, the placenta forms, and body systems and features begin to develop. The term 'fetus' is used towards the end of this trimester as the body structure is essentially formed, but fetal movement in the uterus comes later.
Step-by-step explanation:
During the first trimester, several key developments take place as a new life begins to form. The embryo is moved into the uterus and implants itself into the lining. This period is marked by the embryonic stage, occurring between weeks 3 to 8 after conception. At this time, the placenta forms around the embryo, which is crucial as it provides nourishment and oxygen to the developing embryo through the umbilical cord.
Subsequently, internal organs and other body systems begin their initial formation within the fetus, and basic body features start to become apparent. Around the end of the first trimester, the term 'fetus' is used to describe the developing human, and some body features are clearly formed such as limb buds, eyes, and the liver. However, it is too early for the baby to begin movement in the uterus; this typically occurs during the second trimester.