Abstract
Author(s): Witold Malinowski (ABDEF), Hieronim Bartel (BD)
Recently, the obstetric mantra that “monochorionicity guarantees monozygosity” has been finally overthrown. It has been proven that monochorionic diamniotic dizygotic (MCDADZ) twin pregnancies, sharing the same placenta, do occur, though very rarely. Also in dizygotic twin pregnancies vascular connections may develop between foetuses. Thus, in the twinto- twin transfusion syndrome (TTTS) and in conjoined twins in certain cases foetuses may differ genetically or even be of different sex. This paper analyses possible mechanisms leading to the development of monochorionic diamniotic dizygotic twin pregnancy on a basis of the latest studies.