Editing Multiple birth (section)

==Causes and frequency==
{{Globalize|article|North America|date=December 2010}}
The frequency of ''N'' multiple births from natural pregnancies has been given as approximately 1:89<sup>''N''−1</sup> (''[[Hellin's law]]'') and as about 1:80<sup>''N''−1</sup>.<ref>{{Cite web |last1=Bush |first1=Melissa |last2=Pernoll |first2=Martin L. |date=15 September 2010 |title=Multiple Pregnancy |url=http://www.health.am/pregnancy/multiple-pregnancy/ |website=Pregnancy Health Center |publisher=Health.am}}</ref> This gives:
*1:89 (= 1.1%) or 1:80 (= 1.25%) for twins
*1:89<sup>2</sup> (= 1:7921, about 0.013%) or 1:80<sup>2</sup> (= 1:6400) for triplets
*1:89<sup>3</sup> (= approx. 0.000142%, less than 1:700,000) or 1:80<sup>3</sup> for quadruplets

North American dizygotic twinning occurs about once in 83 conceptions, and triplets about once in 8000 conceptions. US figures for 2010 were:<ref>{{Cite web |title=National Center for Health Statistics - Multiple Births |url=https://www.cdc.gov/nchs/fastats/multiple.htm |archive-url=https://web.archive.org/web/20131020102618/http://www.cdc.gov/nchs/fastats/multiple.htm |archive-date=2013-10-20}}</ref><ref>{{Cite report |url=https://www.cdc.gov/nchs/data/nvsr/nvsr61/nvsr61_01.pdf#table01 |title=Births: Final Data for 2010 |date=August 28, 2012 |publisher=National Vital Statistics Reports |issue=1 |volume=61 |archive-url=https://web.archive.org/web/20170720102442/https://www.cdc.gov/nchs/data/nvsr/nvsr61/nvsr61_01.pdf |archive-date=July 20, 2017}}</ref>
* Twins – 132,562 (3.31%)
* Triplets – 5,503 (0.14%)
* Quadruplets – 313 (0.0078%)
* Quintuplets and more – 37 (0.00092%)

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.<ref name="Beemsterboer-2006">{{Cite journal |vauthors=Beemsterboer SN, Homburg R, Gorter NA, Schats R, Hompes PG, Lambalk CB |year=2006 |title=The paradox of declining fertility but increasing twinning rates with advancing maternal age |journal=Hum. Reprod. |volume=21 |issue=6 |pages=1531–2 |doi=10.1093/humrep/del009 |pmid=16497698}}</ref>

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.{{Citation needed|date=February 2007}} 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 [[Follicle-stimulating hormone|FSH]], followed by intrauterine [[insemination]], are particularly at risk for multiple births of higher order.

[[File:KoreAm 2008-05 Cover.jpg|thumb|right|The Gosselin sextuplets with their parents and sisters, cover of ''[[KoreAm]]'', May 2008]]
Certain factors appear to increase the likelihood that a woman will naturally conceive multiples. These include:
*mother's age: women over 35 are more likely to have multiples than younger women<ref name="www.acog.org">{{Cite web |title=Multiple Pregnancy - ACOG |url=http://www.acog.org/Patients/FAQs/Multiple-Pregnancy#are |url-status=live |archive-url=https://web.archive.org/web/20160111114120/http://www.acog.org/Patients/FAQs/Multiple-Pregnancy#are |archive-date=2016-01-11 |access-date=2016-01-13 |website=www.acog.org}}</ref>
*mother's use of [[fertility drug]]s: approximately 35% of pregnancies arising through the use of fertility treatments such as IVF involve more than one child

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 (TV channel)|TLC]]'' network.