EFFECTS OF PULSED MAGNETIC-FIELDS ON THE DEVELOPING MOUSE EMBRYO

The influence of a pulsed magnetic field (PMF; sawtooth with 45-mus linear rise time and 5-mus decay time, peak strength of 15 muT, and frequency 20 pps) on the embryogenesis of CBA/S mice was investigated in five experiments based on a total of 707 exposed and 543 unexposed primigravidas. Sham and PMF exposures began on day 1 of gestation (experiments 1 and 2), on day 2 (experiment 3), on day 5 (experiment 4), and on day 7 (experiment 5); all exposures continued until day 19 post conception (p.c.), when they were terminated, at which time the following variables were measured: number of implants; number of placental resorptions; number of living fetuses; number of dead fetuses; number of malformations in living and dead fetuses; and length and body mass of living fetuses. Control dams were sham-exposed concurrently with corresponding, PMF-exposed dams. With the exception of experiment 5, in which exposure to PMF started on day 7 p.c., all groups of exposed mice had significantly more placental resorptions when compared with concurrent controls. The increased resorption rate was not reflected in a reduction in litter size or in the number of litters. A significant increase in malformed fetuses was not seen in any of the exposed groups, or when groups were pooled. Only in experiment 1 was the number of dead fetuses affected by exposure to PMF. The effect of PMF on the implantation rate was not significant. Body mass and length of exposed fetuses were significantly reduced only when the PMF treatment began on day 7 p.c. That PMF-treated mice had significantly more placental resorptions when exposure began on day 5 p.c. or earlier (before implantation), but not when exposure began on day 7 (after implantation), may indicate a causative pre-implantation effect. Because a PMF-induced increase in the number of resorptions has not been observed in other strains of mice, the effect might be strain-related.