Editing Superfetation

{{Short description|Simultaneous presence of multiple stages of developing offspring in one animal}}
{{Use dmy dates|date=October 2020}}
'''Superfetation''' (also spelled '''superfoetation''' – see [[fetus]]) is the simultaneous occurrence of more than one stage of developing offspring in the same animal.<ref>{{cite journal|last1=Roellig|first1=K|last2=Menzies|first2=BR|last3=Hildebrandt|first3=TB|last4=Goeritz|first4=F|title=The concept of superfetation: a critical review on a 'myth' in mammalian reproduction.|journal=Biological Reviews of the Cambridge Philosophical Society|date=February 2011|volume=86|issue=1|pages=77–95|doi=10.1111/j.1469-185X.2010.00135.x|pmid=20394608|s2cid=5798316}}</ref><ref name=Mc2016/><ref>{{cite magazine|url=http://content.time.com/time/health/article/0,8599,1926414,00.html|title=How Can a Pregnant Woman Get Pregnant Again?|author=Fletcher, Dan|magazine=Time Magazine|date=28 September 2009|access-date=29 March 2018}}</ref>

In [[mammals]], it manifests as the formation of an embryo from a subsequent menstrual cycle, while another embryo or fetus is already present in the [[uterus]]. When two separate instances of [[fertilisation]] occur during the same [[menstrual cycle]], it is known as [[superfecundation]].

==Humans==
While proposed cases of superfetation have been reported in humans, the existence of this phenomenon in humans has been deemed unlikely.<ref name=Mc2016>{{cite journal|last1=McNamara|first1=HC|last2=Kane|first2=SC|last3=Craig|first3=JM|last4=Short|first4=RV|last5=Umstad|first5=MP|title=A review of the mechanisms and evidence for typical and atypical twinning.|journal=[[American Journal of Obstetrics and Gynecology]]|date=February 2016|volume=214|issue=2|pages=172–191|doi=10.1016/j.ajog.2015.10.930|pmid=26548710}}</ref> Better explanations include differential growth between twins due to various reasons, such as [[twin-to-twin transfusion syndrome]].<ref name=Mc2016/> Artificially-induced superfetation has been demonstrated, although only up to a short period after insemination.<ref name=Mc2016/>

A 2008 French study found evidence to suggest that superfetation is a reality for humans, but that it is so rare that there have been fewer than 10 recorded cases in the world.<ref>{{cite web |title=Superfœtation: about a case and review of the literature |date=4 June 2008 |website=EM Consulte Journal of Obstetrics and Reproductive Biology |url=https://www.em-consulte.com/article/195925/alertePM |first1=O. |last1=Pape |first2=N. |last2=Winer |first3=A. |last3=Paumier |first4=H.J. |last4=Philippe |first5=B. |last5=Flatrès |first6=G. |last6=Boog}}</ref>

In 2017, it was reported that an American woman who had agreed to act as a [[Surrogacy|surrogate]] for a Chinese couple bore two babies, who were initially believed to be twins. Before the adoptive parents could return home to China, however, it was discovered that one of the babies was, in fact, the biological son of the surrogate. Doctors confirmed that the birth-mother had become pregnant with her and her partner's child, roughly three weeks after becoming pregnant with the Chinese couple's child.<ref>{{cite web|url=https://www.insideedition.com/surrogate-mom-gets-pregnant-while-carrying-another-couples-baby-37644|title=Surrogate Mom Gets Pregnant While Carrying Another Couple's Baby|date=30 October 2017|website=Inside Edition |first1=Deborah |last1=Hastings |access-date=16 December 2018}}</ref>

There have been multiple cases in the United States of women who reported twins with a difference in age of a week or less and women who reported two surges of ovulation occurring within a few days of each other. Though rare, this condition is believed to affect as many as 0.3% of women, but one twin is often lost, so the true numbers are not known.{{Citation needed|date=October 2018}}

Research has found that 10% of women release two eggs in a cycle, but both eggs are released at the end of the same "wave" of follicullogenesis, which does not support the theory of superfetation in humans.<ref>{{Cite news|url=https://www.newscientist.com/article/dn3927-women-can-ovulate-more-than-once-a-month/ |date=9 July 2003 |title=Women can ovulate more than once a month|last=Vince|first=Gaia|work=[[New Scientist]]|access-date=2018-10-22|language=en-US}}</ref>

In 2017, a woman in İzmir, Turkey, became pregnant with two babies conceived about a month apart and she gave birth to both on October 7, 2017. According to the news report this event has officially been registered in global medical records as the 12th superfetation case.<ref>{{cite news |url=https://www.hurriyetdailynews.com/turkish-woman-makes-history-as-12th-superfetation-case-172407|title=Turkish woman makes history as 12th superfetation case
|newspaper=[[Hürriyet Daily News]] |date=March 23, 2022 |url-status=live |archive-url=https://web.archive.org/web/20231116175213/https://www.hurriyetdailynews.com/turkish-woman-makes-history-as-12th-superfetation-case-172407 |archive-date= Nov 16, 2023 }}</ref> 

In September 2020, a woman in Wiltshire, England, gave birth to fraternal twins, who were conceived three weeks apart.<ref>{{Cite news |date=2021-04-07 |title=Woman gets pregnant while already pregnant, gives birth to twins conceived 3 weeks apart |url=https://www.washingtonpost.com/lifestyle/2021/04/08/conceive-baby-while-pregnant/ |work=[[The Washington Post]] |language=en-US |url-access=subscription |first1=Sydney |last1=Page |url-status=live |archive-url= https://web.archive.org/web/20231214082110/https://www.washingtonpost.com/lifestyle/2021/04/08/conceive-baby-while-pregnant/ |archive-date= Dec 14, 2023 }}</ref>

==Other animals==
Superfetation is normal for some species of [[poeciliid]] [[fish]]<ref>{{cite web|title=Glossary - superfetation |url=http://www.fishbase.org/glossary/Glossary.php?q=superfetation|access-date=16 December 2018|website=FishBase |url-status=live |archive-url=https://web.archive.org/web/20171206141348/http://www.fishbase.org/glossary/Glossary.php?q=superfetation |archive-date= Dec 6, 2017 }}</ref> and has been clearly demonstrated for the [[European Brown Hare|European brown hare]].<ref>{{Cite web|last1=Zielinski|first1=Sarah|title=Hares Can Get Pregnant While Pregnant|url=https://www.smithsonianmag.com/science-nature/hares-can-get-pregnant-while-pregnant-35542864/ |date= September 23, 2010 |access-date=2021-10-15|website=Smithsonian Magazine|language=en}}</ref>

In [[Domestic Cats|domestic cats]], superfecundation is common, but superfetation never has been definitively proven to occur.<ref>{{Cite journal|last=Root Kustritz|first=Margaret V.|date=2006-07-01|title=Clinical management of pregnancy in cats|journal=Theriogenology|volume=66|issue=1|pages=145–150|doi=10.1016/j.theriogenology.2006.03.018 |doi-access=free |issn=0093-691X|pmc=7103129|pmid=16620942}}</ref>

Animals that have been claimed to be subject to superfetation include [[rodent]]s ([[mouse|mice]] and [[rat]]s), rabbits, [[horse]]s, [[sheep]], [[marsupials]] ([[kangaroo]]s and [[sugar glider]]s), felines, and [[primate]]s ([[humans]]).

==References==
{{Reflist}}

==External links==
* "[https://web.archive.org/web/20160304002427/http://etd.lsu.edu/docs/available/etd-0730102-222405/unrestricted/Carter_dis.pdf Superfetation in Beef Cattle]" doctoral thesis; Joel Andrew Carter, Louisiana State University, defended 18 March 2002
* "[http://www.fishbase.org/glossary/Glossary.php?q=superfetation Superfetation]" at FishBase

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[[Category:Multiple births]]