Dictionary of Human Evolution and Biology

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Multiple Births

Polyembryony in humans is considered to be a clinically exceptional, teratogenic event, the production of multiple embryos from a single fertilized egg, such as monozygous twins. Most higher-order multiples (three or more births) are mixed sets of identical and fraternal twins. The predicted number of natural births (not induced by hormone therapy) of each kind is the subject of Hellin’s law of multiple births. The so-called vanishing twin phenomenon has recently led to a renewed interest in the twin events. Multiple births occur approximately once in every 73 births (incidence is.02725); of these, the majority are twins (94.4%), 5% are triplets, 0.5% are quadruplets, and 0.1% are quintuplets or higher.

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