Final answer:
The first trimester of prenatal development is a critical period when the basic structures of the body are formed.
Step-by-step explanation:
The first trimester of prenatal development is a critical period when the basic structures of the body are formed. During this stage, which lasts for the first 12 weeks of pregnancy, organs and body structures such as limb buds, the heart, eyes, and liver begin to develop. By the end of the first trimester, the fetus is about 5 centimeters in length and many of the organs are not yet functioning. It is important for the pregnant person to receive prenatal care during this stage to reduce health risks to themselves and the developing baby.