Conjoined twins are defined as mono chronic and mono amniotic
twins fused at any portion of their body as a result of an incomplete division of the embryonic disk, which occurs after the 13th day of conception. The term "conjoined" is actually a misnomer, since most authors consider the pathogenesis of the condition to result from failure of complete separation, instead of
fusion of twin. Yet at least one author proposes that the fusion of two normal embryos results in
Conjoined twins This is a rare condition and the reported frequency varies from 0.1-0.35:10,000 births. If stillborns are excluded the estimate is 0.05:10,000. Females are more commonly affected with a male to female ratio of 1.6-3:1. No association with maternal age, race, parity or heredity has ever been observed. The recurrence risk is negligible. Conjoined twins are classified according to the area of the bodies where the fusion takes place and the involvement of internal organs. The symmetrical and equal forms, in which the twins have equal or nearly equal
duplication of structures, are called
duplicata completa. When there is an unequal duplication of structures they are called duplicata incompleta, and this category includes the most severe types of conjoined twins in which just few organs systems are duplicated. The most frequent varieties of conjoined twins are thoracopagus (40%), omphalopagus (33%), pygopagus (18%), ischiopagus (6%) and craniopagus (2%) .
Ultrasound can be a cost effective and the prime modality in diagnosis of
conjoint twins and further characterization. It provides precise information regarding the nature of anomaly. It allows a complete anatomical work up, target approach scanning for associated lethal malformations. A detailed ultrasound examination to exclude the possibility of conjoined twins is a must in all multiple pregnancies.
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