At what stage of gestation is the fetus most radiosensitive?

The period from conception to 3 months gestation is recognized as the time when the fetus is most radiosensitive due to several key developmental factors. During the first trimester, the foundations for major organs and systems are being formed, making this stage crucial for proper development. Rapid cell division and differentiation occur, which makes the fetal tissues highly vulnerable to ionizing radiation. In particular, this sensitivity relates to the potential for causing teratogenic effects, growth retardation, or other developmental anomalies if exposed to harmful radiation levels.

As the pregnancy progresses into the second and third trimesters, the tissues become increasingly differentiated and organized, which contributes to a decrease in radiosensitivity. Hence, while radiation exposure at any time during gestation may have risks, the first trimester is particularly critical due to the significant development that occurs during this stage.