During what stage of pregnancy is a fetus most sensitive to radiation?

The first trimester is a critical period for fetal development, during which the fetus is most sensitive to radiation exposure. During this time, the basic structures and major organs of the fetus are forming. This stage includes the most crucial phases of organogenesis, where rapidly dividing cells are particularly vulnerable to damaging effects caused by radiation.

Exposure to radiation during this early development can lead to a higher risk of teratogenic effects, such as congenital malformations or disruptions in essential developmental processes. Given that the cells are still differentiating and establishing organized structures, even low doses of radiation can have significant implications during this period.

As pregnancy progresses into the second and third trimesters, the risk associated with radiation exposure diminishes to an extent, as the major systems have already developed, though risks still exist. Understanding this sensitivity helps in making informed decisions regarding imaging and radiation exposure during pregnancy.