Zygosity is the degree of identity in the genome of twins.Įggs are fertilized during different acts of intercourse However, males are also more susceptible than females to die in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins. For example, the sex ratio of birth in the US is 1.05 males/female, while it is 1.07 males/female in Italy. The rates for singletons vary slightly by country. Female-male twins: This is the most common pairing (50%), simply by virtue of it encompassing both "female-male" (25%) and "male-female" (25%) twins.Īmong non-twin births, male singletons are slightly (about five percent) more common than female singletons.Male–male twins: Sometimes called fraternal twins (25%).Female–female twins: Sometimes called sororal twins (25%).Less common variants are discussed further down the article.įraternal twins can be any of the following: The vast majority of twins are either dizygotic (fraternal) or monozygotic (identical). Some women intentionally turn to fertility drugs in order to conceive twins. Other factors that increase the odds of having fraternal twins include maternal age, fertility drugs and other fertility treatments, nutrition, and prior births. There is no known genetic link for identical twinning. Women who have a family history of fraternal twins have a higher chance of producing fraternal twins themselves, as there is a genetically linked tendency to hyper- ovulate.
IWORD ORIGIN TWIN FULL
Multiple pregnancies are much less likely to carry to full term than single births, with twin pregnancies lasting on average 37 weeks, three weeks less than full term. North America and Europe have intermediate rates of 9 to 16 twin sets per 1,000 live births.
In South America, South Asia (India, Pakistan, Bangladesh, Nepal), and Southeast Asia, the lowest rates are found only 6 to 9 twin sets per 1,000 live births. In Central Africa, there are 18–30 twin sets (or 36–60 twins) per 1,000 live births. 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, possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side. 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.
0 kommentar(er)
