In earlier studies, there are only a few reports about the connection of CB expression and risk factors of the PTB. Increased CB1 protein level has been shown in women with a spontaneous miscarriage, furthermore higher CB1 levels were observed in preeclamptic placental tissue[57]. Therefore, it seems that a decrease in CB1 and CB1a mRNA level could be connected with, for example, preterm placental abruption, which leads to delivery of the immature fetuses or intrauterine death of the fetus[58]. We have not observed similar effects in our study as no observation of intrapartum CB mRNA levels was performed. Nevertheless, low CB1 and CB1a levels correlated with a history of intrauterine death of the fetus and history of PTB. In the current study, a significant correlation was observed between bleeding in the early stages of the pregnancy with lower CB2 expression. Vaginal bleeding in late pregnancy is the most common early symptom of placental abruption[59]. Bleeding in the first trimester is a known PTB risk factor[60, 61]. Thus, bleeding can be interpreted as a risk of preterm delivery because of extremely early placental abruption. This raises another question - what if the lowering of CB is responsible for extremely preterm (<22 hbd) delivery in the mechanism of placental abruption, presenting as an intrauterine death of the fetus or miscarriage? In this area further investigations seems to be crucial.