The number of multinucleated trophoblastic giant cells in the basal decidua is decreased in retained placenta.

AIMS Retained placenta (RP) is a major cause of obstetric haemorrhage. The aim of the study was to obtain a better understanding of the mechanisms that cause some placentas to become retained, while most are not. METHODS 23 RPs clinically diagnosed as placenta adhesiva and 10 control placentas (CPs) were examined for differences in trophoblast fusion into multinucleated trophoblastic giant cells (MTGCs), defects in the basal decidua, and decidual attachment of myometrial fibres. RESULTS The number of MTGCs in the basal decidua was significantly smaller in RPs (0.23 MTGC/standard length) than in CPs (1.11 MTGC/standard length) (p<0.001). Defects in the decidua were observed in 4% of the RPs and in 0% of the CPs. Myometrial fibres were attached to the decidua in 78% of the RPs and in 0% of the CPs (p<0.001). CONCLUSIONS In placenta adhesiva compared with CPs, significantly less MTGCs were present in the basal decidua, the basal decidua was intact, and myometrial fibres were more frequently attached to the basal decidua. It is speculated that these findings may indicate that defective fusion of trophoblastic cells into MTGCs plays a causative role in placenta adhesiva.