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Definition
By Mayo Clinic staffIdentical (monozygotic) twins occur when a single fertilized egg splits and develops into two fetuses. In a few cases, the fertilized egg fails to separate completely. The babies that develop from this partial separation are called conjoined twins.
Unlike most identical twins, conjoined twins share the same amniotic fluid and placenta. They're also physically connected — most often at the head, chest or pelvis. Conjoined twins may even share one or more internal organs.
Many conjoined twins are stillborn or die shortly after birth. Some surviving conjoined twins can be surgically separated. The success of this surgery depends on where the twins are joined and how many organs are shared, as well as on the experience and skill of the surgical team.
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