During which trimester does the majority of fetal development occur?

The first trimester is critical for fetal development as it encompasses the period from conception to the end of week 12. During this time, the foundational aspects of development take place, including the formation of vital organs and systems. By the end of the first trimester, most major structures are established, such as the heart, brain, spinal cord, and limbs. Additionally, this stage is when significant growth occurs in terms of the embryo transitioning to a recognizable fetus.

The rapid cellular division and differentiation that happen in the first trimester set the stage for the growth and maturation processes that follow in the second and third trimesters. Consequently, while development continues throughout the entire pregnancy, the first trimester is particularly essential as it lays the groundwork for the remaining gestational period.