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TWINNINGS & TWINNINGS & CONJOINTCONJOINTLECTURE BY PROF. ANSARILECTURE BY PROF. ANSARI

(for MBBS students only) (for MBBS students only)

Sunday, November 9th, 2008.Sunday, November 9th, 2008.

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ObjectivesObjectives

Types of twiningTypes of twining Maternal twinsMaternal twins Fraternal twinsFraternal twins Siamese twinsSiamese twins

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Human twins are classified Human twins are classified into two major groups:into two major groups:

MonozygoticMonozygotic (one-egg, or identical) twins and (one-egg, or identical) twins and DDizygoticizygotic (two-egg, or fraternal) twins. (two-egg, or fraternal) twins.

Fraternal twins are the result of two separate Fraternal twins are the result of two separate fertilization events, whereas identical twins are fertilization events, whereas identical twins are formed from a single embryo whose cells formed from a single embryo whose cells somehow dissociated from one another. somehow dissociated from one another.

Identical twins may be produced by the Identical twins may be produced by the separation of early blastomeres, or even by the separation of early blastomeres, or even by the separation of the inner cell mass into two separation of the inner cell mass into two regions within the same blastocyst regions within the same blastocyst

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Identical twins formationIdentical twins formationmonozygotic twinsmonozygotic twins

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Conjoined TwinsConjoined Twins

are identical twins who develop with a single are identical twins who develop with a single placenta from a single fertilized ovum. placenta from a single fertilized ovum.

are always of the same sex and race. are always of the same sex and race. are more often female than male, at a ratio of are more often female than male, at a ratio of

3:1. 3:1. occur as often as once in every 40,000 births occur as often as once in every 40,000 births butbut only once in every 200,000 only once in every 200,000 livelive births. births.

are more likely to occur in India or Africa than are more likely to occur in India or Africa than in China or the United States. in China or the United States.

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Types of Conjoined TwinsTypes of Conjoined Twins

CraniopagusCraniopagus: Cranial union only, about 2% of all conjoined twins. : Cranial union only, about 2% of all conjoined twins.

PygopagusPygopagus: Posterior union of the rump, about 19% of all : Posterior union of the rump, about 19% of all conjoined twins. conjoined twins.

ThoracopagusThoracopagus: Anterior union of the upper half of the trunk. The : Anterior union of the upper half of the trunk. The most common form of conjoined twins (about 35%), it always most common form of conjoined twins (about 35%), it always involves sharing the heart. involves sharing the heart.

CephalopagusCephalopagus: Anterior union of the upper half of the body with : Anterior union of the upper half of the body with two faces on opposite sides of a conjoined head. Extremely rare. two faces on opposite sides of a conjoined head. Extremely rare. The heart is sometimes involved. A combination of types 3 and 4 The heart is sometimes involved. A combination of types 3 and 4 is called is called cephalothoracopaguscephalothoracopagus. .

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ParapagusParapagus:(sometimes called diprosopus): :(sometimes called diprosopus): lateral union of the lower half, extending lateral union of the lower half, extending variable distances upward, about 5% of all variable distances upward, about 5% of all conjoined twins. Heart sometimes involved. conjoined twins. Heart sometimes involved.

IschopagusIschopagus: Anterior union of the lower half of : Anterior union of the lower half of the body, about 6% of all conjoined twins. the body, about 6% of all conjoined twins. Heart not involved. Heart not involved.

OmphalopagusOmphalopagus: Anterior union of the : Anterior union of the midtrunk, about 30% of conjoined twins. midtrunk, about 30% of conjoined twins.

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CraniopagusCraniopagus

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