The Vanishing Twin: Morphologic and Cytogenetic Evaluation of an Ultrasonographic Phenomenon

Rudnicki, M., Vejerslev, L.O., Junge, Jette

Abstract. Twin pregnancy was observed by ultrasonographic examination in the 6th week of gestation. After singleton term delivery a thickening of the membranes opposite to the main placenta showed degenerated chorionic villi embedded between one layer of amnion and chorion; no fetal parts were observed. Villus cells from both placentas were mainly deploid; 2 of 30 were tetraploid. Marker analysis was consistent with duplication of a normal conception diploid chromosome complement as the mechanism for tetraploidy. Postconceptional nondisjunction leading to tetraploidy in one twin conceptus may explain demise in early pregnancy. Tetraploidy observed by chorionic villus biopsy most be confirmed by amniocentesis before interruption of the pregnancy is considered. Gynecol Obstet Invest 1991;31:141-145

At birth the only remnants of a vanishing twin may be fibrous thickening of part of the membranes. The possible difference between chromosome constitution i fetal and extrafetal tissue has important implications for prenatal diagnosis. Further studies of cytogenetic constitution related to histology could increase our understanding of the initial events, the frequency of mono- and dizygotic twinning and the implications of chromosome aberrations in the “vanishing twin”.