This animal study reports results from five experimental campaigns over five years examining weak magnetic field exposure and morphological abnormalities in White Leghorn chick embryos. Four campaigns reported statistically significant increases in abnormality rates, while one pulsed-field campaign showed only a small, non-significant increase. Pooled analyses reported increased abnormality rates for both pulsed and 60 Hz sinusoidal exposures compared with controls, and the authors propose genetic susceptibility as a possible confounder.