multiple birth

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multiple birth,

bringing forth of more than one offspring at birth. Although many smaller mammals bear several young at a time, multiple births are relatively uncommon in humans and other primates. Twinning, the process that leads to the production of more than one offspring, results in twins, and with decreasing frequency, triplets, quadruplets, quintuplets, sextuplets, septuplets, and octuplets.

In the one-egg, or identical, type of twinning, a single fertilized ovum divides to form two complete organisms. Such twins are always of the same sex, are usually extraordinarily similar in physical appearance, and have identical blood-group types. Twinning to form one-egg identical twins usually takes place early in pregnancy. If considerable development has taken place before the twinning occurs, there may be an incomplete separation of the two embryos resulting in conjoined twinsconjoined twins,
congenitally united organisms that are complete or nearly complete individuals, historically known as Siamese twins. They develop from a single fertilized ovum that has divided imperfectly; complete division would produce identical twins, having the same sex and
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. Despite their similarities, identical twins have epigenetic differences that influence how their common DNA is used and expressed.

Fraternal twins, which are more common than identical twins, are those that develop from two separate ova, each fertilized by a sperm. Fraternal twins may or may not be of the same sex and need not resemble each other more than do any other two offspring of the same parents. In the United States twins occur once in approximately 40 births. In rare cases, non-identical embryos can fuse in the womb to produce a condition called chimerism, in which some of the individual's cells come from one of the embryos and the rest of the cells come from the other, genetically distinct embryo.

The incidence of multiple-egg births is in part genetically determined, varying according to race and family tendencies; and it is also influenced by external factors, i.e., the incidence increases with increasing age of the mother and the number of children she has already borne. One-egg, or identical, twinning occurs with the same frequency in all women, regardless of race, age, or other factors. There is evidence from comparative biology that deleterious factors in the environment of the newly fertilized ovum, such as a reduction in oxygen, increase the likelihood of one-egg twinning. Fertility drugsfertility drug,
any of a variety of substances used to increase the possibility of conception and successful pregnancy. Different methods are used to correct or circumvent the many different functional disorders of both males and females that can interfere with conception and
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 such as clomiphene, which are used when the cause of infertility is lack of released ova, sometimes cause several ova to be released and fertilized simultaneously. The use of these drugs has led to a rise in the incidence of multiple births, including sextuplets, septuplets, and octuplets.

References in periodicals archive ?
Fifth: Improving transportation by completing the National Control Center, rehabilitating the Septuplet link station Ksara and completing the building of a high tension network.
The story of the McCaughey septuplets is a quintessentially American story, combining many ingredients of modern life.
Wixted was a consultant to Iowa Methodist Medical Center last fall as it prepared for the birth of the McCaughey septuplets. The medical center expected and received international media attention.
No less a theologian than Secretary of Health and Human Services Donna Shalala has pronounced the birth of septuplets to Bobbi and Kenny McCaughey of Carlisle, Iowa, an act of God.
The first is the septuplet sixteenth which makes an important appearance in the second half of B and is discarded again as the music moves into the [A.sup.1] section.
In the first tableau, the flutes must execute septuplet figures over an ongoing 3/4 meter.
Two-letter words: 7 shiftword pairs; 5 triplets; 2 quadruplets; 3 quintuplets; 4 sextuplets; 1 septuplet Three-letter words: 191 shiftword pairs; 76 triplets; 19 quadruplets; 1 quintuplet Four-letter words: 278 pairs; 11 triplets Five-letter words: 85 pairs; no triplets Six-letter words: 9 pairs; no triplets Seven-letter words: 2 pairs; no triplets The above table illustrates the exponentially increasing unlikelihood of having two conflicting solutions as the number of disks increases beyond five, even if each disk is arranged in a strictly alphabetic order.
Jermaine Jenas (pictured) is another of Jol's exciting septuplet and the pounds 9m former Newcastle man was responsible for the brilliant curling equaliser which pitched the Red Devils into an all-too-familiar state of gloom after Mikael Silvestre had taken advantage of a rare Robinson blunder to put the hosts ahead.
The run rocketed the three-time US Masters and Open winner up the leaderboard, topped on nine-under 129 by a septuplet of relatively unheralded names.
"As a rule, I'm happy when Time and Newsweek have the same thing on their cover and we do something else," Fallows said during an interview with AJR the week his rivals played up the septuplet saga.
For example, in repetition 10, the duration of the W chord remains constant at a quarter note plus a dotted-eighth-note septuplet while the duration of the Z chord moves from a half-note, to a half-note plus an eighth-note quintuplet, and then to a half-note plus a quarter-note quintuplet.
Although there are many meter changes and the aural ambiguity that results from ties and changing subdivisions, the subdivisions are not complicated ones (triplets and sixteenths, and in the strings, one septuplet in a measured trill, and one quintuplet), and they are very easy to read in the computer notation used, as in the rhythmic style and appearance of the Persichetti Parable, but always metered.