Embryonic death, dwarfism and fetal malformations after irradiation of embryos at the zygote stage: studies on two mouse strains.

Female mice of the BALB/c and CF1 strains were mated and irradiated with various doses of X-rays 7 h after presumed fertilization. 18 days later, females were killed and their uteri examined for prenatal mortality at the different stages of development. Living fetuses were weighed and examined for the presence of external malformations. A number of them were also examined for skeletal anomalies. Radiation induced mainly a dose-dependent increase of the preimplantation loss in the BALB/c strain and of the early postimplantation loss in the CF1 strain. Embryos of the BALB/c strain were refractory to the induction of teratogenic effects after such preimplantation irradiation. In CF1 mice, the frequency of malformed fetuses increased regularly after irradiation, the difference with controls being significant for the doses of 10, 50 and 100 cGy. Dwarfism occurrence also appeared to be increased by irradiation in this strain, although the importance of this effect varied depending on the criterion chosen for the assessment of dwarfs. With the definition proposed in the present paper, the increase in the frequency of dwarfs paralleled that of malformed fetuses, being significant after doses of 50 and 100 cGy. Irradiation did not increase the frequency of skeletal anomalies. A careful examination of the various data obtained to data led us to conclude that radiation may possibly be teratogenic in several mouse strains, when administered as early as during the one-cell stage and, to a lesser extent, during the following preimplantation stages. However, early prenatal mortality will remain by far the greatest risk associated with an exposure to radiation during this period. Moreover, the relativity of the risk of abnormality due to such irradiation should be considered in the context of the high prevalence of developmental defects spontaneously occurring during human pregnancy.