The average expression of the CB2 was significantly lower in the study group than in the control group, 26.8 vs. 31.1 (p=0.038), respectively. Lack of CB2 expression in the placentas were more often in the study group, it was 23 vs. 3, respectively, OR= 2.67 (95%CI: 0.75 - 9.48). Moreover, the statistical analysis using U Mann-Whitney test shown correlation between CB2 receptor expression with the occurrence of PTB (p=0.038), what was shown in the Figure 1. Expression of CB1 and CB1a receptors correlates positively with enlarged pain perception of the labour (measured on the VAS scale (R Spearman 0.202, p=0.039 and R Spearman 0.261, p=0.0007, respectively).