The article deals with the peculiarities of the fetal dissociated development in monochorionic and bichorionic placentation according to various ways of the multiple pregnancies beginning. It was determined that dissociation occurred in monochorionic placentation more often. Most often dissociation occurred in group of monochorionic multiple pregnancies induced by in vitro fertilization method. More often dissociated development was present in same-sex twins. The dissociation was not always accompanied by variation of amniotic fluid. Polyhydramnios/oligohydramnios was not always accompanied by arrested development in one of the twins.
