Dose-response relationship between body temperature and birth defects in radiofrequency-irradiated rats.

Five groups of pregnant Sprague-Dawley rats were irradiated for 10-40 min on gestation day 9 in a 27.12-MHz radiofrequency field at a magnetic field strength of 55 A/m and an electric field strength of 300 V/m. The specific absorption rate was 10.8 +/- 0.3 W/kg. Exposures were terminated after the rat's colonic temperature reached 41.0 degrees C, 41.5 degrees C, 42.0 degrees C, 42.5 degrees C, or 43.0 degrees C. A control group was sham irradiated at 0 A/m and 0 V/m on gestation day 9, whereas a second control group was untreated. The incidence of both birth defects and prenatal death was directly related to maternal body temperature once a temperature threshold was exceeded. The temperature threshold for both types of effects was approximately 41.5 degrees C. A few pregnant rats died after exposure to 43.0 degrees C, and higher temperatures were nearly always lethal.