Completion of fetal organogenesis typically occurs by which gestational week?

• A. 8th week
• B. 9th week
• C. 10th week
• D. 12th week

Answer: (C)

Organ development happens rapidly in early pregnancy, with the major organ systems forming mainly in the first trimester. By around the tenth week, those organ structures have formed and the embryo transitions into a fetus; after this point, growth and refinement of tissues occur rather than the creation of new organs. That’s why the tenth week is the typical point used to indicate completion of organogenesis. By week eight you’re still seeing ongoing organ formation in some systems, and by week twelve growth continues but without new organs being established. In ultrasound practice, the tenth week marks when the basic organ layout is in place and the fetus begins more defined maturation.