The expression of CB1, CB1a, CB2 mRNA was found to be present in human placental tissue during pregnancy. The finding that there is lower CB2 expression in PTB placentas is a crucial step which might, in further investigations, lead to the development of a prediction factor of PTB. Further studies are needed to assess the expression of CB during pregnancy. Liquid-based cytology could be used as a noninvasive perinatal method of measuring the expression level of CB in decidual cells during pregnancy.