1 TWINNINGS & CONJOINT LECTURE BY PROF. ANSARI (for MBBS students only) Sunday, November 9th, 2008.

2 Objectives  Types of twining  Maternal twins  Fraternal twins  Siamese twins

3 Human twins are classified into two major groups:  Monozygotic (one-egg, or identical) twins and Dizygotic (two-egg, or fraternal) twins.  Fraternal twins are the result of two separate fertilization events, whereas identical twins are formed from a single embryo whose cells somehow dissociated from one another.  Identical twins may be produced by the separation of early blastomeres, or even by the separation of the inner cell mass into two regions within the same blastocyst

4 Identical twins formation monozygotic twins

5 Conjoined Twins  are identical twins who develop with a single placenta from a single fertilized ovum.  are always of the same sex and race.  are more often female than male, at a ratio of 3:1.  occur as often as once in every 40,000 births but only once in every 200,000 live births.  are more likely to occur in India or Africa than in China or the United States.

6 Types of Conjoined Twins  Craniopagus: Cranial union only, about 2% of all conjoined twins.  Pygopagus: Posterior union of the rump, about 19% of all conjoined twins.  Thoracopagus: Anterior union of the upper half of the trunk. The most common form of conjoined twins (about 35%), it always involves sharing the heart.  Cephalopagus: Anterior union of the upper half of the body with two faces on opposite sides of a conjoined head. Extremely rare. The heart is sometimes involved. A combination of types 3 and 4 is called cephalothoracopagus.

7  Parapagus:(sometimes called diprosopus): lateral union of the lower half, extending variable distances upward, about 5% of all conjoined twins. Heart sometimes involved.  Ischopagus: Anterior union of the lower half of the body, about 6% of all conjoined twins. Heart not involved.  Omphalopagus: Anterior union of the midtrunk, about 30% of conjoined twins.

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9 Craniopagus

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