Which trimester is critical for the development of major organs in the fetus?

The first trimester is critical for the development of major organs in the fetus because this is when foundational growth and organogenesis occur. During this period, many of the essential systems, such as the heart, brain, and spinal cord, begin to form. This stage lasts from conception up until approximately 12 weeks of gestation, and it is during this time that the embryo undergoes rapid development and differentiation of cells into the various organ systems.

By the end of the first trimester, the main structures of the body have been established, setting the stage for further growth and maturation in the subsequent trimesters. The significant changes and vulnerability associated with the first trimester underscore its importance; exposure to teratogens, nutritional deficiencies, or other harmful factors can significantly impact organ development and may lead to congenital abnormalities.

In contrast, while the second and third trimesters involve growth and maturation of the organs, the foundational processes predominantly occur in the first trimester.