Influence of ionizing radiation on fetoplacental growth in mice

The effects of single doses of 60Co whole-body irradiation were studied in about 600 inbred primiparous Swiss-Webster mice on gestational day 9, 10, 11, or 12. The embryos and their placentas were weighted from day 13 to 18. A reference model surveyed the response of the conceptus to varying doses. A significant reduction in the fetal wet weight was observed as follows: day 9, 150 to 175 R; day 10, 125 to 150 R; day 11, 75 to 175 R; day 12, 125 to 450 R. Beyond the upper-limit doses, a high mortality rate was detected, i.e., 64.5 percent on day 10 at 175 R and 63 percent on day 11 at 200 R. The rapid growth period of the placenta extended from day 13 to 15. By this latter stage it had practically reached its maximum development. The placental index decreased progressively from day 13 to 18; however, this index was higher than the control on day 12 in treated animals, while lower on day 9, 10, or 11