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 ?
FERTILITY treatment is leading to a rise in the multiple birth rate, especially among women over 45, according to new figures.
Children of multiple births also means additional financial burden to the parents, doubling or tripling the expenses for every child as they grow older, and more so if they have disabilities," said Colmenares.
The continued decline in higher-order multiple births is a key finding, and one that confirms clinical improvements in a number of areas, Dr Ball said in an interview.
They expressed that they are so used to dealing with singleton births that the complexities of multiple births are often overlooked'.
The AFA has a long-standing commitment to educating patients about eSET in order to reduce twin and high-order multiple births," stated Ken Mosesian, Executive Director.
7 multiple births per 1,000 women in 2010 - which is a rise of 6.
Multiple births also had higher rates of pre-term births (from the total of all single births only 7.
Although singleton and multiple births share some similarities, there are some striking physical, psychological, economic, ethical, and medical differences (Leonard & Denton, 2006; Miller, Ransom, Shalhoub, Sokol, & Evans, 2000; Pector, 2005).
TWINS and triplets from across the region came together to celebrate multiple births yesterday.
Keith Reed, chief executive of the Twins and Multiple Births Association (Tamba), said parents were not getting specific education on multiple pregnancies - putting pregnant women and their children at risk.
Scientists have now officially recorded that this area produces the highest incidence of natural multiple births in the world.

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