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The human twin birth rate in the United States rose 76% from 1980 through 2009, from 9.4 to 16.7 twin sets (18.8 to 33.3 twins) per 1,000 births. [5] The Yoruba people have the highest rate of twinning in the world, at 45–50 twin sets (90–100 twins) per 1,000 live births, [6] [7] [8] possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may ...
Monochorionic twins are monozygotic (identical) twins that share the same placenta. If the placenta is shared by more than two twins (see multiple birth ), these are monochorionic multiples . Monochorionic twins occur in 0.3% of all pregnancies. [ 1 ]
Monoamniotic twins are always monochorionic and are usually termed Monoamniotic-Monochorionic ("MoMo" or "Mono Mono") twins. [1] [2] They share the placenta, but have two separate umbilical cords. Monoamniotic twins develop when an embryo does not split until after formation of the amniotic sac, [1] at about 9–13 days after fertilization. [3]
The Hayes also have two sets of twins, Kevin and Kyle (eight years old at the time of the sextuplets' birth) and Kieran and Meghan (five years old). They are the only family in the United States to have two sets of twins and a set of sextuplets. [93] The family was the subject of a reality television show, Table for 12, on TLC in the U.S. [94]
Dizygotic (fraternal) twins can be caused by a hyperovulation gene in the mother. [8] Although the father's genes do not influence the woman's chances of having twins, he could influence his children's chances of having twins by passing on a copy of the hyperovulation gene to them. Monozygotic (identical) twins do not run in families.
Nearly half (8 of 17) of twins examined in one study were monozygotic (identical) twins, a few more than the average of 30%. [4] Twin births were noted from the early twentieth century, when the first immigrants included seventeen sets of twins, and have been observed through several generations in the latter part of the twentieth century. [6]
The power of twin designs arises from the fact that twins may be either identical (monozygotic (MZ), i.e. developing from a single fertilized egg and therefore sharing all of their polymorphic alleles) or fraternal (dizygotic (DZ), i.e. developing from two fertilized eggs and therefore sharing on average 50% of their alleles, the same level of genetic similarity found in non-twin siblings).
A vanishing twin, also known as twin resorption, is a fetus in a multigestation pregnancy that dies in utero and is then partially or completely reabsorbed. [ 1 ] [ 2 ] In some instances, the dead twin is compressed into a flattened, parchment-like state known as fetus papyraceus .