Effects of high environmental temperatures on the development of rabbit embryos.

Hyperthermia was induced in pregnant rabbits (day 9 of gestation) by placing them in an incubator at 45 degrees C. The rabbits were killed on day 29 of gestation, the fetuses were inspected for organ malformations macroscopically and for skeleton malformations microscopically. The results were compared with those of control animals (without hyperthermia). The rise in temperature up to 3 degrees C above the normal value resulted in a significant higher malformation and resorption rate. These findings are in contrast to previous experiments having shown that virally induced fever (day 9 of gestation) results in no anomalies of development.