When does major organogenesis occur in the developing fetus?

Major organogenesis occurs during the period of 2 to 8 weeks after conception, which is why this choice is the correct answer. During this critical phase of development, the foundations for all the major organs and systems of the body are established. This period is crucial as the embryo undergoes significant changes, with organ systems beginning to form and differentiate.

During weeks 2 to 8, the embryo transitions from a simple structure into a more complex form where primary structures such as the heart, brain, and spinal cord begin to take shape. This is also when key developments occur in areas such as limb formation and the establishment of the gastrointestinal system.

Recognizing this time frame is essential for understanding prenatal development because any disruptions or teratogenic exposures during these weeks can lead to significant congenital anomalies. Thus, the period of 2 to 8 weeks after conception is acknowledged as the most crucial time for organogenesis in human development.