Teratogenic and lethal effects of 2–24 h hyperthermia episodes on chick embryos

Hyperthermia is a proven teratogen, inducing malformations and embryonic death in humans as well as in laboratory animals. The aim of our study was to define temperatures that are teratogenic after short-term exposure (from 2 to 24 h) on embryonic days 1–7 and to detect critical periods for the origin of structural defects in the chick embryo. Hyperthermia of 41 °C was not embryotoxic, temperatures from 42 to 44 °C induced malformations and embryonic death, while nearly all embryos died even after the shortest exposures to 45 or 46 °C. Among the wide spectrum of observed malformations, only ventricular septal defect (VSD) and caudal regression syndrome (CRS) were present at frequencies significantly different from those seen in controls.