Effects of in utero exposure to 4.7 T MR imaging conditions on fetal growth and testicular development in the mouse

The effects of exposure in utero to high field (4.7 T) magnetic resonance imaging (MRI) conditions on fetal growth, adult growth, and testicular development in the mouse were investigated. Exposures of 8-h duration were made on day 9 and/or day 12 of gestation. Also investigated were effects of a combined treatment regime using continuous wave, unfocussed 1 MHz ultrasound on day 9 and MRI on day 12. Treatment groups consisted of 8 to 10 pregnant dams. Fetal data were taken on day 18 of gestation and data from adult animals that were exposed in utero were taken on day 50 postpartum. Significant differences in sensitive biological end points following in utero exposure to complex MRI field conditions were found. Fetal weights of the exposed groups ranged from 11% (day 9 MRI) to 17% (day 9 ultrasound/day 12 MRI) lower ( p ≤ .05) than those of the cage control and sham-exposed fetuses and crown-rump length of exposed animals was reduced by 8% ( p ≤ .05). The postpartum death rate was as high as 38% (significant at p ≤ .05 level) following MRI exposure on day 9 and day 12 of gestation. Daily sperm production was reduced by as much as 44% ( p ≤ .05) in adults exposed to MRI on day 12 of gestation. A reduction in testis weight and volume in the adult males was also seen, but the difference was not statistically significant at the p ≤ .05 level. No effect was seen on embryonic deaths, sex ration, body weight at day 50, spleen weight, or seminal vesicle weight. The mechanism responsible for these results could involve one or more of the applied fields interacting with a sensitive stage of fetal development. Further studies are planned to isolate the individual field components and to elucidate biochemical and/or hormonal changes that may follow in utero exposure.