Conjoined twins

Conjoined twins are identical twins born with bodies physically connected because their embryonic development did not fully separate. The connection may involve skin, organs, or other tissues.

Monozygotic twins: Twins that develop from one fertilized egg that divides into two embryos. Conjoined twins are a rare outcome of development from a single fertilized egg.
Incomplete fission theory: A hypothesis that conjoined twins form when a single embryo incompletely splits into two embryos. It is a classic explanation for the persistent physical connection.
Prenatal diagnosis: The identification of fetal conditions before birth using imaging, screening, or diagnostic tests. Ultrasound and fetal imaging can identify connection sites and shared structures.
Chang and Eng Bunker: Siamese-American brothers born conjoined in 1811 who became internationally known performers and entrepreneurs. Their lives shaped the historical association between conjoined twins and the phrase “Siamese twins.”
Embryonic development: The process by which an embryo forms and develops its tissues and organs. The timing and pattern of early development shape where bodies remain connected.
Fusion theory: A hypothesis that conjoined twins form when initially separate embryonic tissues fuse. It offers an alternative to incomplete separation as an explanation of connection.
Fetal ultrasonography: Medical imaging of a fetus using high-frequency sound waves. It is commonly used to detect conjoined twins and assess their anatomy during pregnancy.
Daisy and Violet Hilton: British-born conjoined twin sisters who became performers in vaudeville and film. Their public careers show how performance and exploitation intersected in the history of conjoined twins.
Primitive streak: A transient structure in an early embryo that establishes body axes and initiates gastrulation. Its formation and regression are central to leading explanations of conjoined twinning.
Parasitic twin: An asymmetrical form of conjoined twinning in which one twin is severely underdeveloped and dependent on the other. It illustrates how shared development can produce markedly unequal anatomy.

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