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Related to twins: fraternal twins


Two offspring from a single pregnancy. Twins may be derived from a single fertilized egg that separates into two after the first division. Such monozygotic twins are genetically identical. Alternatively, twins may be derived from two eggs fertilized at the same time. Such twins are dizygotic and non-identical and in about half the cases are of different sex. The rate of monozygotic twinning in humans is fairly stable at 0.35 per cent, while the rate of dizygotic twinning varies more widely around an average of 1 per cent of pregnancies.


two offspring born at the same time of the same mother. See DIZYGOTIC TWINS, MONOZYGOTIC TWINS.


two offspring produced in the same pregnancy. See also dizygotic and monozygotic twins (below).

conjoined t's
fused, symmetrical twins formed by incomplete division of one embryo into two components. See also siamese twins.
discordant t's
a particular trait is present in only one of the twins.
dissimilar twins
dizygotic twins (below).
dizygotic t's
those that develop from two separate ova fertilized at the same time. They may be of the same sex or of opposite sexes, and are no more similar than any other two offspring of the same parents. Called also fraternal, binovular, dichorial, dissimilar and unlike twins.
fraternal t's
dizygotic twins.
free symmetrical monozygotic t's
see identical twins (below).
identical t's
derived initially from a single zygote; placentas may be shared or separate.
impacted t's
twins so situated during delivery that pressure of one against the other produces simultaneous engagement in the birth canal of both.
induced twins
produced experimentally in ruminants using PMSG or FSH, or by immunization against androstenedione.
monovular twins
see monozygotic twins (below).
monozygotic t's
those which develop from a single ovum that divides after fertilization. Because they share the same set of chromosomes, they are always of the same sex, and are remarkably similar in haircoat color and pattern, teeth, and other respects. Monozygotic twins have exactly the same blood type and can accept tissue or organ transplants from each other. May be free and symmetrical, free and asymmetrical, cojoined and symmetrical or cojoined and asymmetrical. Called also identical, enzygotic, monochorial, mono-ovular, similar, or true twins.
Siamese t's
cojoined twins. See also siamese twins.
similar twins
see monozygotic twins (above).
symmetrical t's
twins of equal size, age and stage of development.
true twins
see monozygotic twins (above).
unequal t's
twins of which one is incompletely developed, called also asymmetric twins.
unlike twins
see dizygotic twins (above).

Patient discussion about twins

Q. anything a mother should know about the last period of twin pregnancy? she is in her 7th month and starting to be real heavy... her legs hurt like crazy. anything to help her with?

A. thanks for all the information! I hope everything will go on well...

Q. Is there a bigger risk of autism for the newborn in twin pregnancy?

A. thanks Dominicus!
you're great...

More discussions about twins
References in periodicals archive ?
As the twin brother tried to figure about his life, the twin sister stated that it was something for the famous actor and no one was a famous actor.
Although some epidemiological studies have reported that there was no difference in the risk of perinatal complications according to the birth order, recent studies have shown that the risk of perinatal mortality and neonatal morbidity was high in the second twin than the first twin, and the inter twin delivery interval have been suggested as an important risk factor associated with incidence of delivery related complications in second twins7-9.
Local doctor Dr Krishnan Sribiju said: "In my medical opinion there are around 300 to 350 twins within the village boundaries of Kodinhi.
The rate for identical twins is random and universal (no influencing factors) and occurs one in every 285 births.
As a twin herself, with fraternal twin sons and identical twin nieces, Friedman is a prime candidate to write a book on the emotional dynamics of twins.
Has your study of twins influenced your position on the nature/nurture debate?
If there is some urgency in finding out if the twins are identical, detailed blood typing, DNA fingerprinting and tissue (HCA) typing can be done.
However, the number of differences increased with the age of the twins examined.
For numerous reasons, conjoined twins have long been of medical, historical, and legendary interest.
In a study involving 14 transverse and 11 breech second twins, at least 70% in each group underwent successful version, and success was not related to gestational age or birth weight.
Scotland, for example, currently has 125,00 twins who account for 2.