Irradiation damage to the embryo, fetus, and neonate

Radiation during preimplantation stages probably produces no abnormalities in survivors, owing to the great developmental plasticity of very early mammalian embryos. Radiation at later stages may, however, produce morphologic abnormalities, general or local growth retardation, or functional impairments if doses are sufficient. Obvious malformations are particularly associated with irradiation during the period of major organogenesis which in man extends approximately from week two through week nine after conception. More restricted morphologic and functional abnormalities and growth retardations dominate the spectrum of radiation effects produced during the fetal and early post-natal periods. Some of these effects can be apparent at birth and others may show up later; subtle functional damage cannot be adequately measured with available techniques. Because the central nervous system is formed during a relatively long period in human development, such abnormalities as microcephaly and mental retardation figure prominently among the list of radiation effects reported in man. Animal data indicate that readily measurable damage can be caused by doses well below 10 R of acute irradiation applied at stages that are sensitive to specific effects being studied