Radiation effects on pre-natal development and their radiological significance.

The evidence relating to pre-natal radiation exposure and the subsequent occurrence of malformations and cancer suggests that the overall risk lies in the range 0--1 cases per 1000 irradiated by one rad in utero in the first four months of pregnancy. The natural level of occurrence of serious handicaps in average pregnancies is at least 30 times higher. Is the much lower probability of radiation-induced harm sufficiently high to justify (a) concern when a woman who has been irradiated is found to have been pregnant at that time, or (b) the maintenance of restrictions on medical uses of ionizing radiation in women in the reproductive age, such as the ten day rule?