Objective: to reveal the morphological features of placentas and to define a role of the lectin pathway for activation of the complement system in the development of premature birth. Material and methods. A complex morphological study was conducted to examine 37 placentas, 25 of which were obtained from women with clinical signs of threatened miscarriage and 12 placentas from apparently healthy pregnant women. Results. Placental tissue CD59 expression was ascertained to be significantly less in the women with threatened miscarriage than in those having full-term babies. Conclusion. Decreased CD59 expression in threatened miscarriage at late gestational ages leads to additional activation of a maternal immune response and serves as a possible predictor for premature birth.