An increased incidence of congenital malformations is seen in up to 7% of twin gestations (compared to 3% in singletons). The anomalies usually affect only one twin, although the incidence of chromosomal abnormality in monozygotic twinning with different phenotypes should always be considered.

·         CNS abnormalities, including neural tube defect, hydrocephalus, holoprosencephaly

·         Congenital heart disease

·         Chromosomal abnormality

·         Cloacal extrophy

·         Sacrococcygeal teratoma

·         Sirenomelia.

                                                                      Fig. 1 Sirenomelia