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Monochorionic-monoamniotic twins

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Monozygotic twins that share the same chorion and amniotic sac


Twins may be classified according to the degree of separation in utero, i.e. according to chorionicity (placentae) and amniocity (i.e. number of amniotic sacs): (1) dichorionic-diamniotic twins, (2) monochrorionic-diamniotic twins, (3) monochorionic-monoamniotic twins, and (4) conjoined twins.

In monochorionic-monoamniotic (MoMo) twins, the twins share the same chorion and amniotic sac in utero. They may share the same placenta and amniotic sac but they separate umbilical cords.

The survival rate is about 50% to 60%.1 MoMo twinning is associated with risks such as twin-to-twin transfusion syndrome. It is when one twin receives more of the nourishment than the other resulting in the other's undernourishment. There is also a high risk that the umbilical cords of the fetuses would be tangled around them. Thus, there is a probability of miscarriage or cerebral palsy due to lack of oxygen caused by cord entanglement.

This type of twinning develops when the split takes place after day 9 post-fertilization, when the amniotic sac has formed.2

See also:

1 Twin. Retrieved from [[1]].
2 Shulman, L. S. and Vugt, J. M. G. van (2006). Prenatal medicine. Washington, DC: Taylor & Francis. pp. 447.