Postnatal investigation of prenatally induced effects on the vertebral column of rats reduces the uncertainty of classification of anomalies.

Classification of substances as teratogenic is based on the observation of external, visceral and skeletal anomalies. Characterization of anomalies as variation or malformation is contingent upon their postnatal persistence and adversity to health. Lack of information thereof may result in inconsistent or incorrect classification. The aim of this work is the examination of vertebral skeletal anomalies regarding their postnatal fate on PNDs 7 and 21. The anomalies unossified, asymmetric ossification, bipartite ossification, hemicentric, as well as misshapen, did not persist up to PND21 and should be classified as a variation. The finding, cervical vertebra centrum dumbbell-shaped, should be categorized as a malformation due to its continued presence on PND 21. Lumbar centrum supernumerary sinister/dexter/sinister+dexter should also be classified as a malformation. This study demonstrates that postnatal examination is useful and substantially improves the ability to perform a scientifically sound classification of an anomaly compared to investigations terminated on GD 21.