Influence of gender and body hemisphere on the occurrence of wavy ribs: An analysis of spontaneous skeletal abnormalities in Wistar rat fetuses

The differentiation of background findings from anomalies relevant for the safety evaluation of a future drug is a major task in the interpretation of developmental toxicity studies. The anomaly wavy rib often occurs in litters exposed to the test substance, but is also frequently present in control litters. Therefore, the relevance of this finding for risk assessment is under discussion. We characterized the skeletal morphology of fetuses with wavy ribs from our background data. Differences in the incidence of wavy ribs between the genders, with approximately twice as many male fetuses having wavy ribs, compared to females, and an overrepresentation of the right body hemisphere were observed. Affected fetuses often occurred clustered in single litters. The presented data might be useful for differentiation of spontaneously occurring wavy ribs from abnormal patterns induced by a test substance.