Twins Health Dictionary

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Twins: From 3 Different Sources

Two offspring resulting from one pregnancy. Monozygotic, or identical, twins develop when a single fertilized egg divides at an early stage of development. Incomplete division of the egg results in conjoined twins (see Siamese twins). Monozygotic twins share the same placenta. Dizygotic twins develop when 2 eggs are fertilized at the same time. They each have a placenta and may be of different sexes. Twins occur in about 1 in 80 pregnancies. (See also pregnancy, multiple.)
Health Source: BMA Medical Dictionary
Author: The British Medical Association
pl. n. two individuals who are born at the same time and of the same parents. Fraternal (or dizygotic) twins are the result of the simultaneous fertilization of two egg cells; they may be of different sexes and are no more alike than ordinary siblings. Identical (or monozygotic) twins result from the fertilization of a single egg cell that subsequently divides to give two separate fetuses. They are of the same sex and otherwise genetically identical; any differences in their appearance are due to environmental influences. All dizygotic twins and about one-third of monozygotic twins are dichorionic (i.e. they develop within separate chorionic membranes). About two-thirds of monozygotic twins are monochorionic, sharing a chorion. See chorionicity. See also conjoined twins.
Health Source: Oxford | Concise Colour Medical Dictionary
Author: Jonathan Law, Elizabeth Martin

Siamese Twins

See CONJOINED TWINS; MULTIPLE BIRTHS.... siamese twins

Conjoined Twins

Identical twins who are united bodily but are possessed of separate personalities. Their frequency is not known, but it has been estimated that throughout the world, six or more conjoined twins are born every year who are capable of separation. The earliest case on record is that of the ‘Biddendon Maids’ who were born in England in 1100. The ‘Scottish Brothers’ lived for 28 years at the court of James III of Scotland. Perhaps the most famous conjoined twins, however, were Chang and Eng, who were born of Chinese parents in Siam in 1811. It was they who were responsible for the introduction of the term, ‘Siamese twins’, which still remains the popular name for ‘conjoined twins’. They were joined together at the lower end of the chest bone, and achieved fame by being shown in Barnum’s circus in the United States. They subsequently married English sisters and settled as farmers in North Carolina. They died in 1874.

The earliest attempt at surgical separation is said to have been made by Dr Farius of Basle in 1689. The ?rst successful separation in Great Britain was in 1912: both twins survived the operation and one survived well into adult life. This is said to be the ?rst occasion on which both twins survived the operation. The success of the operation is largely dependent upon the degree of union between the twins. Thus, if this is only skin, subcutaneous tissue and cartilage, the prospects of survival for both twins are good; but if some vital organ such as the liver is shared, the operation is much more hazardous. (See MULTIPLE BIRTHS.)... conjoined twins

Dizygotic Twins

Two people born at the same time to the same parents after fertilisation of two separate oöcytes (see OÖCYTE). They may be of di?erent sexes and are no more likely to resemble each other than any other sibling pairs.... dizygotic twins

Identical Twins

See MULTIPLE BIRTHS.... identical twins

Monozygotic Twins

Twins who develop from a single OVUM fertilised by a single SPERMATOZOON. Also known as identical or uniovular twins (see MULTIPLE BIRTHS).... monozygotic twins

Binovular Twins

Twins who result from the fertilisation of two separate ova. (See MULTIPLE BIRTHS.)... binovular twins

Twins, Conjoined

Identical twins physically joined due to a failure to separate during development from a single fertilized egg.

Also called Siamese twins.... twins, conjoined

Fraternal Twins

see twins.... fraternal twins

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