Fetal sensitivity to ionizing radiation is highest during which time period of pregnancy?

• A. Weeks 2-15
• B. First trimester
• C. Second trimester
• D. Third trimester

Answer: (A)

Fetal sensitivity to ionizing radiation is greatest during the period of rapid cell division and organ formation, when tissues are most vulnerable to disruption. This critical window spans roughly from the second week through the fifteenth week after conception. During these weeks, many organs are developing and differentiating, so radiation exposure can more readily lead to congenital anomalies and neurodevelopmental effects if the dose is significant. After this window, the fetus becomes less susceptible to malformations from radiation, although there can still be risks at higher doses. So the period from about two to fifteen weeks of gestation is when radiation exposure poses the highest potential for developmental impact.