During which trimester does organogenesis occur in human embryonic development?

Organogenesis is a crucial phase in human embryonic development during which the organs and major systems of the body begin to form. This process primarily occurs in the first trimester, specifically from approximately the third week to the end of the eighth week of pregnancy. During this period, the three germ layers—ectoderm, mesoderm, and endoderm—differentiate and develop into various organs and structures.

The first trimester is foundational for the overall development of the embryo, as it sets the stage for further growth and maturation of the systems established during organogenesis. By the end of this trimester, most of the major organs are in place, although they continue to develop and mature throughout the remainder of the pregnancy. Understanding the timing of organogenesis is crucial for comprehending how embryonic development progresses and the potential impact of teratogens (environmental factors that can cause developmental malformations) during this vulnerable period.