[Placental findings in "vanishing twins"]

We examined morphologically the placenta in 15 cases of a "vanishing-twin" phenomenon of early pregnancy sonographically confirmed. In 10 of these cases remnants of an additional gestation product could be identified with ample variation in their conservation. These ranged between macerated, but clearly identifiable foetal residues and morphologically regular, empty gestational sacs, all being localised at the placental margin or within the amniotic tissue sheets. The chorionic villi of the surviving twins were normally developed. There was no evidence of any correlation between the developmental status of the vanished twin and any therapeutical intervention, age of the mother or number of initial gestational products. In 3 cases, an intrauterine foetal reduction by foetocide had been performed. In these instances, rather well-developed remnants of the additional fetuses could be found. Since in all cases a pluri-chorionic placenta was present, it is possible, that the vanishing twin phenomenon may be held responsible for an eventual blood group incompatibility during subsequent pregnancies.