What kind of twinning_?

Thoraco-omphalopagus with omphalocele with parasitic twin. Conjoint twin or Siamese twins result when incomplete division of the egg occurs late after day 14 post conception. As the differentiation of the chorion and amnion has occurred hence conjoined twins are seen only in monochorionic monoamniotic twins. {1} The incidence is very low and occurs in 1 in 50,000 births to 1 in 1,00,000 out of which incidence of parasitic twins is only 10 percent. Most of them are found to be females. Survival depends on extent of which vital organs are shared. {1} Conjoined twinning occurs by the incomplete splitting of the embryonic axis and, with the exception of parasitic conjoined twins, all are symmetrical and the same parts are always united to the same parts. {2} Most common site of fusion is chest and, or abdomen. In one of the study it was found that the most common varieties were thoraco-omphalopagus {28 percent}, thoracopagus {18.5 percent}, omphalopagus {10 percent}, parasitic twins {10 percent} and craniopagus {6 percent}. {2} Survival is 80-90 percent in twins that undergo elective surgery. {1}

Last Updated: June 2012 Vol 9 Issue 6 Art # 37

References :

Enciso J. Multiple births. In: Cloherty J, Eichenwald E, Stark A, eds. Manual of Neonatal Care. 6th ed. New Delhi: Lippincott Williams and Wilkins. 2008:91 Kaufman MH. The embryology of conjoined twins. Childs Nerv Syst. 2004; 20: 508-525.