multiple birth

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Related to Multiple gestation: polyhydramnios, Multiple pregnancies

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 ?
Maternal morbidity and mortality associated with multiple gestations.
Sood V Chellani H, Arya S, Guliani BP Changing spectrum of retinopathy of prematurity (ROP) and variations among siblings of multiple gestation.
Older age at childbearing and increased use of fertility therapies and ovulation-inducing drugs are driving the spike in multiple gestations.
LEGAL COMMENTARY: The court defined the term as follows: "Birth-related neurological injury means injury to the brain or spinal cord of a live infant weighing at least 2,500 grams for a single gestation, or in the case of a multiple gestation, a live infant weighing at least 2,000 grams at birth cause by oxygen deprivation or mechanical injury occurring in the course of labor, delivery, or resuscitation in the immediate post-delivery period in a hospital, which renders the infant permanently and substantially mentally and physically impaired.
Also, the presence of common comorbidities, such as prematurity and multiple gestation, among some of the first hierarchical conditions, diminished their role in the hierarchy (see Table 4).
Patients excluded from the study had multiple gestation, fetal malformation, allergy to progesterone, missed follow-up, preterm rupture of membranes, or therapeutic premature delivery.
Multiple gestation is a well-recognized risk factor for PTB, increasing the risk of this complication up to 6-fold.
Callahan TL, Hall JE, Ettner SL et al: The economic impact of multiple gestation pregnancies and the contribution of assisted reproductive techniques to their incidence.
The rationale for moving to aromatase inhibitors is that this class of drugs is thought to have fewer antiestrogenic side effects, including a lower risk of ovarian hyperstimulation syndrome and a lower risk of multiple gestation.
Women were not eligible to participate if they were younger than 18, had evidence of psychosis or had been institutionalized because of emotional problems or mental retardation; if the newborn was unlikely to survive; or if there was a multiple gestation.

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