Effects of radiation on growth of caudal vertebrae of mouse fetus

A total of 333 pregnant mice (ddY strain) and their 2759 fetuses were used. When the radiation-induced delay of ossification was used as an indicator of radiation effects on fetal growth, the gestation ages 8 and 16 days were found to be two radiosensitive stages. The degree of the delay of ossification was enhanced with increasing the radiation dose. However, the radiation-induced delay, estimated from the number of ossificated caudal vertebrae on day, was only slightly dependent on the dose rate (1 R/min to 100 R/min). The number of ossificated caudal vertebrae in response to fetal irradiation was paralleled to the body weight of fetus.