Multiple births are birth where more than one baby is born per pregnancy. There are several kinds of multiple births such as twins, triplet, and quadruplets. Twins occur about once in 100 pregnancies, triplets occur about once in 10,000 pregnancies, and quadruplets occur about once in 600,000 pregnancies.
There are two types of twins, identical twins and non identical twins or fraternal twins. Identical twins have the same identity and sex because they are from a single egg and a single sperm and divided into two embryos. Non identical twins or fraternal twins may be the same sex or different sexes and have different identities because they are from 2 eggs and 2 sperm.
Siamese twins or conjoined twins are always identical twins, joined in some part of their body such as the hip, chest, abdomen, buttocks, or head. Some of them may share internal organs such as a heart, brain, or liver. Siamese twins occur about once in 50,000 pregnancies, and only 40% of them live. In the United States, 40 Siamese twins are born each year. Every conjoined twin is called Siamese twins because the most famous conjoined twins were born in Siam (Thailand today). People called Siamese twins after Siam.
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last updated: June 21, 2000
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