Nonthermal effects of mobile-phone frequency microwaves on uteroplacental functions in pregnant rats

Exposure to high-density microwaves can cause detrimental effects on the testis, eye, and other tissues, and induce significant biologic changes through thermal actions. To examine nonthermal effect of continuous wave (CW) 915 MHz microwaves used in cellular phones, we compared the effects of microwaves with those of heat. Thirty-six pregnant rats were assigned to six groups: rats exposed to microwaves at 0.6 or 3 mW/cm² incident power density at 915 MHz for 90 min, rats immersed in water at 38 or 40 °C, which induces about the same increase in colonic temperature of 1.0 or 3.5 °C as 0.6 or 3 mW/cm² microwaves, respectively; rats immersed in water at 34 °C, which is considered to be thermoneutral; and control rats. We identified significant differences in the uteroplacental circulation, and in placental endocrine and immune functions between pregnant rats immersed in water at 34 and 38 °C, but not between rats immersed at 38 °C and those exposed to microwaves at 0.6 mW/cm². By contrast, we observed significant decreases in uteroplacental blood flow and estradiol in rats exposed to microwaves at 3 mW/cm² as compared with those immersed in water at 40 °C. These results suggest microwaves at 0.6 mW/cm² at 915 MHz, equal to a specific absorption rate (SAR) of 0.4 W/kg, which is the maximum permissible exposure level recommended by the American National Standards Institute (ANSI), do not exert nonthermal effects on blood estradiol and progesterone, on splenic natural killer cell activity, on the uteroplacental circulation.