Teratogenic effects are another form of somatic effects of radiation due to malformations of cells, tissues, or organs of a fetus exposed in utero. The effect is well known; children born to highly irradiated mothers exhibit abnormally small heads, and mental retardation and decreased IQ have been observed in children exposed in utero at Hiroshima and Nagasaki. Teratogenic effects can result from radiation overexposure of an embryo or fetus