MMP9 and dystocia: Intriguingly, these data show that the loss of one or two alleles of Mmp9 to the Mmp2-KO background (i.e., Mmp2−/−Mmp9+/− and dKO) leads to a somewhat reversed phenotype of a decreased dystocia incidence (40-42.9%) in relation to the rate in the Mmp2−/− females (54.5%) (Figure 1D).