Identifying and reporting dystocia in laboratory rodents

Dystocia (prolonged, difficult, and/or delayed parturition) results from a variety of potential clinical conditions including uterine inertia, hormonal imbalances, oversized fetuses, abnormal orientation of fetuses in the birth canal, etc. In the laboratory, dystocia frequently results in euthanasia. In 2020, the Health and Environmental Sciences Institute's Developmental and Reproductive Toxicology committee formed a working group to discuss anecdotal reports of increased incidence of dystocia amongst laboratory rodents. Based on an initial survey completed by contributing laboratories, it became apparent that there is significant disparity in how various laboratories define, record, report, and interpret dystocia in laboratory animals. This report highlights the key findings from a survey of performing laboratories conducted by this working group and proposes best practices and recommendations for the monitoring and recording of parturition and dystocia in reproductive toxicity studies in rodents. Implementing consistent definitions, observation strategies, and documentation standards will strengthen data comparability and enhance the scientific foundation on which regulatory decisions are made. Furthermore, consistent reporting of dystocia across industry laboratories will improve the transparency and reliability of evidence used in hazard identification and risk assessment and thereby help reduce discrepancies in regulatory outcomes and facilitate regulatory decision-making for chemicals, plant protection products, biocides, and pharmaceuticals.