Promoting the "3Rs" principle in developmental biology with early and convenient diagnosis of pregnancy in mice.

The 3Rs stand for Replacement of animals in experiments, Reduction in the number of experimental animals, and Refinement of experiments to minimize animal pain and stress. We propose to address Reduction and Refinement in the use of mice as experimental models in developmental research. This study focuses on the maternal percentage of weight increase at gestational day 8 (%WI(GD8)) to diagnose pregnancy early in BALB/c mice. We documented sensitivity, specificity, false positive and negative rates and probability of pregnancy associated with %WI(GD8). This predictive model of pregnancy allows for significant reduction in the number of mice to be sacrificed in developmental research. Reported observations and literature suggest that this model is independent of litter size and should be applicable to other mice strains. This procedure allows mice pregnancy detection before midgestation and proposes an ethically sound approach to experimental animal use by optimizing the number of mice used and refining animal manipulation.