Final answer:
The most sensitive trimester to radiation during pregnancy is the first trimester, particularly the embryonic stage where critical development occurs. Exposure to radiation can lead to somatic and genetic damage, with heightened risk to rapidly dividing cells like those in embryos.
Step-by-step explanation:
The trimester of pregnancy that is deemed to be the most sensitive to radiation is the first trimester, especially during the embryonic stage. During this time, the major events of gastrulation, neurulation, and organogenesis occur. This leads to the creation of the three germ layers, the nervous system, and most of the organs of the human body. Therefore, exposure to radiation during this period can cause severe damage or even death of the embryo.
It is crucial to understand that radiation exposure can have both somatic and genetic damage. The effects are more pronounced in cells that reproduce rapidly, such as those in embryos. This is why radiation therapy during pregnancy requires particular care to avoid potential risks to the developing fetus.