Multiple birth
A multiple birth is the culmination of one multiple pregnancy, wherein the mother gives birth to two or more babies. A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies. Such births are often named according to the number of offspring, as in twins and triplets. In non-humans, the whole group may also be referred to as a litter, and multiple births may be more common than single births. Multiple births in humans are the exception and can be exceptionally rare in the largest mammals.
"Triplets" redirects here. For other uses, see Triplet.
A multiple pregnancy may be the result of the fertilization of a single egg that then splits to create identical fetuses, or it may be the result of the fertilization of multiple eggs that create fraternal ("non-identical") fetuses, or it may be a combination of these factors. A multiple pregnancy from a single zygote is called monozygotic, from two zygotes is called dizygotic, or from three or more zygotes is called polyzygotic.
Similarly, the siblings themselves from a multiple birth may be referred to as monozygotic if they are identical or as dizygotic (in cases of twins) or polyzygotic (for three or more siblings) if they are fraternal, i.e., non-identical.
Each fertilized ovum (zygote) may produce a single embryo, or it may split into two or more embryos, each carrying the same genetic material. Fetuses resulting from different zygotes are called fraternal and share only 50% of their genetic material, as ordinary full siblings from separate births do. Fetuses resulting from the same zygote share 100% of their genetic material and hence are called identical.[1] Identical twins are always the same sex.
Terms used for the number of offspring in a multiple birth, where a number higher than three ends with the suffix -uplet:
Terms used for multiple births or the genetic relationships of their offspring are based on the zygosity of the pregnancy:
Multiple pregnancies are also classified by how the fetuses are surrounded by one or more placentas (chorionicity) and amniotic sacs (amnionicity).[2]
The frequency of N multiple births from natural pregnancies has been given as approximately 1:89N−1 (Hellin's law) and as about 1:80N−1.[28] This gives:
North American dizygotic twinning occurs about once in 83 conceptions, and triplets about once in 8000 conceptions. US figures for 2010 were:[29][30]
Human multiple births can occur either naturally (the woman ovulates multiple eggs or the fertilized egg splits into two) or as the result of infertility treatments such as in vitro fertilization (several embryos are often transferred to compensate for lower quality) or fertility drugs (which can cause multiple eggs to mature in one ovulatory cycle).
For reasons that are not yet known, the older a woman is, the more likely she is to have a multiple birth naturally. It is theorized that this is due to the higher level of follicle-stimulating hormone that older women sometimes have as their ovaries respond more slowly to FSH stimulation.[31]
The number of multiple births has increased since the late 1970s. For example, in Canada between 1979 and 1999, the number of multiple birth babies increased 35%. Before the advent of ovulation-stimulating drugs, triplets were quite rare (approximately 1 in 8000 births) and higher-order births much rarer still. Much of the increase can probably be attributed to the impact of fertility treatments, such as in-vitro fertilization. Younger patients who undergo treatment with fertility medication containing artificial FSH, followed by intrauterine insemination, are particularly at risk for multiple births of higher order.
Certain factors appear to increase the likelihood that a woman will naturally conceive multiples. These include:
Women conceiving multiples over the age of 35 increase the risk of having fetuses with certain conditions and complications that are not as common in women who are pregnant.
The increasing use of fertility drugs and consequent increased rate of multiple births has made the phenomenon of multiples more frequent and hence more visible. In 2004 the birth of sextuplets, six children, to Pennsylvania couple Kate and Jon Gosselin helped them to launch their television series, originally Jon & Kate Plus 8 and (following their divorce) Kate Plus 8, which became the highest-rated show on the TLC network.
Risks[edit]
Premature birth and low birth weight[edit]
Babies born from multiple-birth pregnancies are much more likely to result in premature birth than those from single pregnancies. 51% of twins and 91% of triplets are born preterm, compared to 9.4% in singletons.[33] 14% of twins and 41% of triplets are even born very preterm, compared to 1.7% in singletons.[33]
Drugs known as betamimetics can be used to relax the muscles of the uterus and delay birth in singleton pregnancies.[34] There is some evidence that these drugs can also reduce the risk of preterm birth for twin pregnancies, but existing studies are small. More data is required before solid conclusions can be drawn.[35] Likewise, existing studies are too small to determine if a cervical suture is effective for reducing prematurity in cases of multiple birth.[36]
As a result of preterm birth, multiples tend to have lower birth weight than singletons. Exceptions are possible, however, as with the Kupresak triplets, born in 2008 in Mississauga, Ontario, Canada. Their combined weight was 17 lbs, 2.7 oz, which set a world record. Two of the triplets were similar in size and, as expected, moderately low birth weight. The two combined weighed 9 lbs, 2.7 oz. The third triplet, however, was much larger and weighed 8 lbs. individually.[37]
Cerebral palsy[edit]
Cerebral palsy is more common among multiple births than single births, being 2.3 per 1,000 survivors in singletons, 13 in twins, and 45 in triplets in North West England.[38] This is likely a side effect of premature birth and low birth weight.
Behavioral issues[edit]
Premature birth is associated with a higher risk for a breadth of behavioral and socioemotional difficulties that begin in childhood and continue through teenagehood and often into adulthood. Conditions where the risk is greatest include attention deficit hyperactivity disorder, autism spectrum disorder, and anxiety disorders.[39]
Ethics of multiple births[edit]
Medically assisted procreation[edit]
In vitro fertilization (IVF) was first successfully completed in the 1970s as a form of assisted reproductive technology. Out of all the assisted reproductive technology available that is currently in practice, in vitro fertilization has the highest chance of producing multiple offspring. Per each female egg, IVF currently has a 60–70% chance of conceiving. Fertilization is made possible by administering a fertility drug to the eggs or by directly injecting semen into the eggs.[32] There is an increased chance for women over the age of 35 to have multiple births.[31] IVF is a common genetic and ethical topic. Through IVF individuals can produce offspring successfully when natural procreation is not viable. However, in vitro can become genetically specific and allow for the selection of particular genes or expressible traits to be dominantly present in the formed embryo.[64] Ethical dilemmas arise when determining health care coverage and the deviation from natural selection and gene variations. In regards to multiple births different ethical concerns arise from the use of in vitro fertilization. Overall, multiple pregnancies can cause potential harm to the mother and children due to potential complications. Such complications can include uterine bleeding and children not receiving equal nutrients.[65] IVF has also revealed some pre term deliveries and lower birth weights in babies.[66] While some view medically assisted procreation as a saving grace to have children, others consider these procedure to be unnatural and costly to the community.
Multifetal pregnancy reduction[edit]
Multifetal pregnancy reduction is the reduction of one or more embryos from the bearing woman. Selective reduction usually occurs for pregnancies assisted by assisted reproductive technology (ART). The first multifetal pregnancy reductions to occur in a clinical setting took place in the 1980s. The procedure aims to reduce pregnancies down to approximately one to two fetuses. The overarching purpose of the procedure is not primarily to simply terminate life, but to increase the survival and success of the mother and babies. However, multifetal pregnancy reduction raises some ethical questions. The main argument is similar to abortion ethics in reduction of fetus versus fetus life. The protection of maternal well being versus harm of newly formed fetal life is an extension of the aforementioned ethical question.[67] It can be viewed that all life is important and that no life should be terminated without consent from the life that is being terminated. A polar opposite viewpoint advocates for the right of choice, that being the choice to terminate a pregnancy due to desire or pregnancy risks.[68] Overall, most multifetal pregnancy reductions that occur as a result of ART are being done for the protection of the child-bearer's health and to maximize the health of the remaining fetuses.[61]