Hazards and Risks from Prenatal Irradiation: Emphasis on Internal Radionuclide Exposures

Irradiation during gestation produces dose- and stage-dependent effects including teratisms, prenatal or neonatal mortality, and altered size, structure, or function of the foetus and its organs. The general effects from internal radionuclide and external irradiation exposures are similar, as are the underlying physical processes and pathogenesis. Radionuclides involve stage-related differences in placental transfer and deposition, and deliver differential radiation doses to extra-embryonic structures and progenitor tissues. Despite differences in likelihoods, delayed effects with either exposure modality include growth depressions, shortened life span, and altered morphology or function of organs, especially the central nervous system. Dose-related increased tumour incidences of pituitary, thyroid, bone, liver, and haematopoietic tissues have been identified in offspring after perinatal exposures of animals. Not all of these have been found in human populations, while other effects, such as mental retardation, do not have distinct correlates in laboratory animals. This paper summarises the consensus on risk and threshold dose ranges, suggests magnitudes of dose for other alterations, and integrates overall patterns of aetiological events and their relationships to effects.