Common fetal aberrations and their teratologic significance: a review

Fetal aberrations occurring at a greater incidence in the test than in the control groups make it difficult to estimate human safety from animal data. This is due to lack of agreement on the teratologic significance of aberrations and our ignorance of mechanisms governing their appearance. Quite often the aberrations are transitory and tend to disappear on further development. A requirement for specially designed studies exists in order to determine the true nature of aberrations and their effects on postnatal development. Only then will it be possible to establish a scientific basis for using animal data to estimate human safety. This review will illustrate the need with examples: changes in the ossification of sternum (which may be retarded by factors remotely related to a test chemical), presence of hydronephrosis (which cannot be diagnosed accurately owing to extreme physiological variations in size of the renal pelvis) and presence of supernumerary ribs (a fetal variation which has been inconsistently interpreted). Relatively little is known about the significance of bent or wavy ribs and undescended testes. Future research should be directed towards determining the teratologic significance, if any, of these and other embryological deviations occurring in experimental animals.