We describe a rare case of acardius in a triplet pregnancy terminated by Caesarean Section at 32 weeks gestation. Morphological and chromosomal abnormalities of the fetus as well as structural abnormalities of the placenta are presented. Cytogenetic analysis and examination of the single disc triplet placenta provide evidence for the two major theories of pathogenesis of acardius, the twin reversed arterial perfusion (TRAP) sequence and the genetic theory, which we believe are not necessarily mutually exclusive.

A holoacardius from a monozygotic, monochorionic twin pregnancy of 36 weeks is described. Trisomy-18 was diagnosed in the viable female cotwin. Computerized tomographic, radiologic, and ultrasonographic procedures were applied to the acardiac. Its three-vessel umbilical cord was velamentously attached to the single placenta. Grossly malformed and poorly developed craniofacial structures, absence of neck and upper extremities, sirenomelic lower extremity, absence of heart, and development of only a few skeletal elements were prominent features. A review of selected world literature emphasizes the limits of the estimates dealing with the total number of reported cases and the incidence of acardii.

A total of 178 placentas of twins born in Tokyo in 1961-1982 were examined. Only just over one third were dichorionic, 110 being monochorionic and DZ twins were estimated to account for 24.7% of the pairs. The lower frequency of DZ twinning in Japan is attributed to lower gonadotropin values in Japanese women as compared to European, American, or African women. High fetal morbidity was found in monochorionic twins and this is attributed to a frequent occurrence of vascular anastomoses.