Higher Order Multiples
High orders of multiple births (three or more offspring in one birth) may result in a combination of fraternal (genetically different) and identical (genetically identical) siblings. The latter are also called super twins. For example, a set of triplets may consist of two identical siblings and one fraternal sibling. This happens when two eggs are fertilized and one of these subsequently divides into two fetuses. By analogy with monozygotic and dizygotic twins, such a combination is called dizygotic triplets. The Kübler triplets (see Elisabeth Kübler-Ross) were of this type.
Identical triplets or quadruplets are very rare and result when the original fertilized egg splits and then one of the resultant cells splits again (for triplets) or, even more rarely, a further split occurs (for quadruplets). Alternatively the original fertilized egg can split twice (to produce four embryos) and all four may survive, to produce identical quadruplets, or one of the embryos may not survive and result in triplets.
Read more about this topic: Multiple Births
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“If twins are believed to be less intelligent as a class than single-born children, it is not surprising that many times they are also seen as ripe for social and academic problems in school. No one knows the extent to which these kind of attitudes affect the behavior of multiples in school, and virtually nothing is known from a research point of view about social behavior of twins over the age of six or seven, because this hasn’t been studied either.”
—Pamela Patrick Novotny (20th century)