Previous studies on animal models revealed similar results to those of our study, reinforcing the potential relevance of CBRs in PTB. Sun et al. observed that a lower expression of the CNR2 gene correlated with PTB in mice [44]. Another study on the mouse model also showed that decreased CBR2 and increased CBR1 expression were associated with PTB. In that study, PTB occurred due to preterm induction with a lipopolysaccharide [34]. Wang et al. showed a positive correlation between decreased CBR1 expression in the placenta of mice and PTB [45].