Twin

Twins are two offspring produced by the same pregnancy.[2] Twins can be either monozygotic ("identical"), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic ("fraternal"), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.[3]

In contrast, a fetus that develops alone in the womb is called a singleton, and the general term for one offspring of a multiple birth is multiple.[4] Non-related look-alikes whose resemblance parallels that of twins are referred to as doppelgangers.[5]

Statistics

The human twin birth rate in the United States rose 76% from 1980 through 2009, from 18.8 to 33.3 per 1,000 births.[6]

The Yoruba peoples have the highest rate of twinning in the world, at 45–50 twin sets (or 90–100 twins) per 1,000 live births,[7][8][9] possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side.[10][11]

In Central Africa, there are 18–30 twin sets (or 36–60 twins) per 1,000 live births.[12] In Latin America, South Asia, and Southeast Asia, the lowest rates are found; only 6 to 9 twin sets per 1,000 live births. North America and Europe have intermediate rates of 9 to 16 twin sets per 1,000 live births.[12]

Multiple pregnancies are much less likely to carry to full term than single births, with twin pregnancies lasting on average 37 weeks, three weeks less than full term.[13]

Women who have a family history of fraternal twins have a higher chance of producing fraternal twins themselves, as there is a genetically linked tendency to hyper-ovulate. There is no known genetic link for identical twinning.[14] Other factors that increase the odds of having fraternal twins include maternal age, fertility drugs and other fertility treatments, nutrition, and prior births.[15] Some women intentionally turn to fertility drugs in order to conceive twins.[16]

Other Languages
Afrikaans: Tweeling
العربية: توأم
ܐܪܡܝܐ: ܬܐܡܐ
asturianu: Ximielgu
Avañe'ẽ: Membykõi
azərbaycanca: Əkiz
বাংলা: যমজ
български: Близнаци
Boarisch: Zwinling
bosanski: Blizanac
brezhoneg: Gevell
català: Bessó
čeština: Dvojčata
chiShona: Mapatya
Cymraeg: Gefell
dansk: Tvilling
Deutsch: Zwillinge
eesti: Kaksikud
Ελληνικά: Δίδυμος
Esperanto: Ĝemelo
euskara: Biki
فارسی: دوقلو
français: Jumeau
Gàidhlig: Leth-aon
galego: Xemelgo
한국어: 쌍둥이
հայերեն: Երկվորյակներ
हिन्दी: जुड़वाँ
hrvatski: Blizanci
Ido: Jemelo
Bahasa Indonesia: Kembar
עברית: תאומים
қазақша: Егіз
Kiswahili: Mapacha
Kreyòl ayisyen: Jimo
Кыргызча: Эгиздер
Latina: Gemini
latviešu: Dvīņi
Lëtzebuergesch: Zwilling
lietuvių: Dvyniai
lingála: Lipása
magyar: Ikrek
मराठी: जुळे
Bahasa Melayu: Kembar
Mìng-dĕ̤ng-ngṳ̄: Sĕ̤ng-săng-giāng
日本語: 双生児
norsk: Tvilling
norsk nynorsk: Tvilling
oʻzbekcha/ўзбекча: Egizaklar
ਪੰਜਾਬੀ: ਜੌੜੇ
português: Gêmeos
română: Geamăn
Runa Simi: T'ira
русский: Близнецы
Scots: Twin
sicilianu: Giameddu
Simple English: Twin
کوردی: دووانە
српски / srpski: Близанац
srpskohrvatski / српскохрватски: Blizanac
suomi: Kaksoset
svenska: Tvillingar
татарча/tatarça: Игезәкләр
తెలుగు: కవలలు
ไทย: แฝด
Türkçe: İkizler (tıp)
українська: Близнюки
اردو: جڑواں
Tiếng Việt: Sinh đôi
Winaray: Karoha
ייִדיש: צווילינג
Yorùbá: Ìbejì
粵語: 孖生
Zazaki: Dıgan
中文: 雙胞胎