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 ?
But closer inspection reveals that it is badly neglected and the octuplets are crammed into bunk beds in a room where the wind whistles in through a dangerously smashed window.
But she insists she has now found God and is planning to stay celibate until her octuplets turn 18.
The more challenging patterns are usually the ones with a displacement of one tick, such as the 5-pattern in sextuplets, the 7-pattern in sextuplets, or the 9-pattern in octuplets.
Suleman attained worldwide notoriety this year when she gave birth to the world's longest-surviving set of octuplets Jan.
When word of the Suleman octuplets reached the newborn intensive care unit at Kaiser Permanente Hospital in Bellflower, California, the physicians, nurses, and other staff recognized that the stabilization and subsequent monitoring of the octuplets would be highly specialized.
The healthy arrival of the Suleman octuplets came as sunny news in bleak times.
So, it was for money and publicity after all (Doctor faces probe over octuplets birth, GDN, February 8).
I know now that I may or may not have really deep down wanted that many siblings, but at the time I was so focused and fixated on wanting so many that I just kept going" - Nadya Suleman, the mother who gave birth to octuplets in the US.
Summary: The octuplets born to a US mother who already had six children have been shown to the world for the first time.
You'll be hearing much more from this unusual woman from Los Angeles once the publicity machine starts whirring around the octuplets to which she gave birth on January 26.
THE mother of octuplets said she was "fixated" on having children, as pictures of the babies aired for the first time.