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Written by Administrator
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The three most common variations are all fraternal:male-female twins are the most common result,at about 40% of all twins born;female fraternal twins (sometimes called sororal twins)male fraternal twins. The last two are identical female identical twins and (least common) male identical twins. Male singletons are slightly, about 5%, more common than female singletons. However, males are also more susceptible than females to death in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins.
Another variety of twins, "polar body twins," (one egg fertilized by two different sperm) is a phenomenon that was hypothesized to occur and may recently have been proven to exist. Polar body twinning would result in "half-identical" twins
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