HETEROKARYOTYPIC MONOZYGOTIC TWINS AND THE ACARDIAC MONSTER

Summary Two acardiac monsters occurring in monozygous diamniotic monochorionic twin pregnancies are described. In one case chromosome analysis of the acardius failed. In the other case fibroblast cultures showed that the acardius had G-trisomy whereas its twin had normal chromosomes. The demonstration of heterokaryotypic monozygosity supports the concept that the acardiac monster is a monozygous twin with a lethal primary defect whose survival in utero is permitted solely by placental anastomoses which allow its normal twin to provide a circulation.