How can radiation exposure during pregnancy contribute to congenital malformations?

Ionizing radiation can cause congenital malformations because embryonic tissues are composed of rapidly proliferating cells, which are highly sensitive to radiation damage. When exposure occurs while a specific organ is forming, the destruction of progenitor cells can interfere with normal development, leading to malformations.12

The specific outcome depends heavily on the timing of exposure during gestation:

• Early embryonic life: Exposure is more likely to be lethal to the embryo than to cause malformations.2
• Organogenesis: Exposure during the period of organ formation is most likely to result in structural malformations.12
• Later stages: Exposure is more likely to produce functional abnormalities rather than structural defects.2

The nervous system is particularly vulnerable; for instance, studies of children exposed in utero during the atomic bombings of Hiroshima and Nagasaki showed an increased incidence of reduced head size and intellectual disability, especially when exposure occurred between the 8th and 15th weeks of pregnancy. The risk of malformation is highest when a dose is received during the critical, sharply circumscribed period of an organ's development.12