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Twins are by far the most common form of multiple births in humans. The U.S. Centers for Disease Control and Prevention report more than 132,000 sets of twins out of 3.9 million births of all kinds each year, about 3.4%, or 1 in 30. [5] Compared to other multiple births, twin births account for 97% of them in the US. [6]
This is a list of multiple births, consisting of notable higher order (4+) multiple births and pregnancies. Twins and triplets are sufficiently common to have their own separate articles. With the use of reproductive technology such as fertility drugs and in vitro fertilization (IVF) such births have become increasingly common. This list ...
Hellin's law, also called Hellin-Zeleny's law, is an empirical observation in demography that the approximate rate of multiple births is one n-tuple birth per 89 n-1 singleton births: twin births occur about once per 89 singleton births, triplets about once per 89 2, quadruplets about once per 89 3, and so on.
A multiple pregnancy (e.g., twins, triplets, etc.) is counted as 1. Parity, or "para", indicates the number of births (including live births and stillbirths) where pregnancies reached viable gestational age. A multiple pregnancy (e.g., twins, triplets, etc.) carried to viable gestational age is still counted as 1. [3]
Natural fertility is a concept developed by the French historical demographer Louis Henry to refer to the level of fertility that would prevail in a population that makes no conscious effort to limit, regulate, or control fertility, so that fertility depends only on physiological factors affecting fecundity.
Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse, which can lead to twin babies from two separate biological fathers.
These studies suggest that the human sex ratio, both at birth and as a population matures, can vary significantly according to a large number of factors, such as paternal age, maternal age, multiple births, birth order, gestation weeks, race, parent's health history, and parent's psychological stress. Remarkably, the trends in human sex ratio ...
Multiple birth, because having twins is sometimes called having "multiples" Multiple sclerosis, an inflammatory disease; Parlance for people with multiple identities, sometimes called "multiples"; often theorized as having dissociative identity disorder; Multiple myeloma (MM), a cancer that forms in a type of white blood cell (WBC) called ...