Only a few studies have been published in recent years where the correlation between labour and CBR expression was observed. Park et al. found a high expression of the CBR1 in the human placenta and an even higher expression in the amniotic epithelium, reticular cells and the cells of the maternal decidua layer [46]. Kozakiewicz et al. showed that the ECS played a role in childbirth via the expression of the CBR1 [47]. However, the role of CBR expression as a potential predictor for PTB in humans remains unexplored. This information might have important implications for clinical practice. Therefore, further studies are needed to assess the expression of CBRs during pregnancy.