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, and early genetic mutations typically result in some small genetic differences between identical twins.

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.

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References in periodicals archive ?
Al Baluchi, father of 3-year-old twin Fatma and Sarah, said: "We invite all multiple birth babies and children to participate in the gathering and in the national march that embodies our love of our homeland.
'We were receiving many reports of mothers giving birth to twins or triplets in the hospitals and the fathers running away because they were scared of how they were going to settle the bills of their obligations, she said.' She added that the Multiple Birth Trust Fund supported no fewer than 740 families between 2010 and 2014.
Multiple birth pregnancies carry more risks than single births because women have a higher chance of miscarriage, premature birth, and babies with cerebral palsy.
Khyber Pakhtunkhwa has seen a dramatic rise in the number of multiple births. According to a report, in 2015 alone, the province recorded a total of 1165 multiple gestations and major hospitals calculated 26 cases of quadruplets, 158 cases of triplets, and over 900 cases of twins.
The rate of multiple births increased to 16 per 1,000 women giving birth, compared with 15.6 in 2013.
But NHS cutbacks, coupled with the quantity of multiple births, has lead to many women not getting the specialist care they need.
The number of multiple births from assisted reproductive technology continues to decline, with no more than 1% of women undergoing the procedures delivering triplets or higher orders of multiples in 2011.
They couldn't understand that I might choose to work or need to work." Because these types of expectations only make multiple birth parents' worries about finances more complicated, this mother and her husband added, "Continued employment for both spouses should be a welcomed and an understandable option."
In 2005, one in every 35 kindergarteners was a multiple birth sibling.
He said: "The number of multiple birth pregnancies has increased dramatically in the last three decades."
"Doctors are refining those advances, and now fewer eggs are implanted with each cycle, reducing the risk of multiple birth" said Long.
Multiple birth resulting from ovarian stimulation for subfertility treatment.

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