A note on the epidemiology of acardiac monsters.

The literature on acardiac monsters has been reviewed. The following conclusions were drawn: 1. The probability of their appearance seems considerably higher among monoamniotic than diamniotic monochorionic twin pairs. 2. They seem more likely to occur within monozygotic (MZ) pairs in higher multiple births than in MZ twins. 3. The data are consistent with the suggestion that there is a slight female excess among them.