EFFECTS OF PULSED MAGNETIC-FIELDS ON THE DEVELOPING MOUSE EMBRYO

The influence of a pulsed magnetic field (PMF; sawtooth with 45-mus li near rise time and 5-mus decay time, peak strength of 15 muT, and freq uency 20 pps) on the embryogenesis of CBA/S mice was investigated in f ive experiments based on a total of 707 exposed and 543 unexposed prim igravidas. Sham and PMF exposures began on day 1 of gestation (experim ents 1 and 2), on day 2 (experiment 3), on day 5 (experiment 4), and o n day 7 (experiment 5); all exposures continued until day 19 post conc eption (p.c.), when they were terminated, at which time the following variables were measured: number of implants; number of placental resor ptions; number of living fetuses; number of dead fetuses; number of ma lformations in living and dead fetuses; and length and body mass of li ving fetuses. Control dams were sham-exposed concurrently with corresp onding, 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 concurren t controls. The increased resorption rate was not reflected in a reduc tion in litter size or in the number of litters. A significant increas e in malformed fetuses was not seen in any of the exposed groups, or w hen groups were pooled. Only in experiment 1 was the number of dead fe tuses affected by exposure to PMF. The effect of PMF on the implantati on rate was not significant. Body mass and length of exposed fetuses w ere 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), b ut not when exposure began on day 7 (after implantation), may indicate a causative pre-implantation effect. Because a PMF-induced increase i n the number of resorptions has not been observed in other strains of mice, the effect might be strain-related.