A study was made by Miller in 1954 of children who were in utero and within 2,200 meters from the hypocenter at the time of the atomic bomb in Hiroshima. These earlier observations have with few exceptions been validated by this follow-up of the subjects at 20 years of age and the value and accuracy of clinical evaluation in early childhood is clearly indicated. The following conclusions are made.
Both small head size (circumference minus 2 SD or more) and mental retardation are most closely related to (1) maternal exposure within 1,500 meters from the hypocenter, and (2) a gestational age of less than 15 weeks.
The heads of infants with either small or normal circumferences at birth increase thereafter in circumference at the same rate and stop growing at the same age, thereby maintaining the same size relationships throughout childhood into adult life.
Mortality in the mentally retarded group as a whole exceeds mortality in normal children. For the group of all subjects exposed within 1,500 meters the mortality rate is higher than for the subjects located beyond 1,500 meters.