{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,24]],"date-time":"2026-10-24T02:12:25Z","timestamp":1792807945618,"version":"4.5.0"},"reference-count":42,"publisher":"Oxford University Press (OUP)","issue":"6","license":[{"start":{"date-parts":[[2021,3,12]],"date-time":"2021-03-12T00:00:00Z","timestamp":1615507200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"name":"European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme","award":["No 681546"],"award-info":[{"award-number":["No 681546"]}],"id":[{"id":"https:\/\/ror.org\/0472cxd90","id-type":"ROR","asserted-by":"crossref"}]},{"name":"Nuffield College, and the Leverhulme Trust","id":[{"id":"https:\/\/ror.org\/012mzw131","id-type":"ROR","asserted-by":"crossref"}]},{"name":"French Agence Nationale de la Recherche","award":["ANR-18-CE36-0007-07"],"award-info":[{"award-number":["ANR-18-CE36-0007-07"]}],"id":[{"id":"https:\/\/ror.org\/00rbzpz17","id-type":"ROR","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2021,5,17]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>STUDY QUESTION<\/jats:title>\n                    <jats:p>How many twins are born in human populations and how has this changed over recent decades?<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>SUMMARY ANSWER<\/jats:title>\n                    <jats:p>Since the 1980s, the global twinning rate has increased by a third, from 9.1 to 12.0 twin deliveries per 1000 deliveries, to about 1.6 million twin pairs each year.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>WHAT IS KNOWN ALREADY<\/jats:title>\n                    <jats:p>It was already known that in the 1980s natural twinning rates were low in (East) Asia and South America, at an intermediate level in Europe and North America, and high in many African countries. It was also known that in recent decades, twinning rates have been increasing in the wealthier parts of our world as a result of the rise in medically assisted reproduction (MAR) and delayed childbearing.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>STUDY DESIGN, SIZE, DURATION<\/jats:title>\n                    <jats:p>We have brought together all information on national twinning rates available from statistical offices, demographic research institutes, individual survey data and the medical literature for the 1980\u20131985 and the 2010\u20132015 periods.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>PARTICIPANTS\/MATERIALS, SETTING, METHODS<\/jats:title>\n                    <jats:p>For 165 countries, covering over 99% of the global population, we were able to collect or estimate twinning rates for the 2010\u20132015 period. For 112 countries, we were also able to obtain twinning rates for 1980\u20131985.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>MAIN RESULTS AND THE ROLE OF CHANCE<\/jats:title>\n                    <jats:p>Substantial increases in twinning rates were observed in many countries in Europe, North America and Asia. For 74 out of 112 countries the increase was more than 10%. Africa is still the continent with highest twinning rates, but Europe, North America and Oceania are catching up rapidly. Asia and Africa are currently home to 80% of all twin deliveries in the world.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>LIMITATIONS, REASONS FOR CAUTION<\/jats:title>\n                    <jats:p>For some countries, data were derived from reports and papers based on hospital registrations which are less representative for the country as a whole than data based on public administrations and national surveys.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>WIDER IMPLICATIONS OF THE FINDINGS<\/jats:title>\n                    <jats:p>The absolute and relative number of twins for the world as a whole is peaking at an unprecedented level. An important reason for this is the tremendous increase in medically assisted reproduction in recent decades. This is highly relevant, as twin deliveries are associated with higher infant and child mortality rates and increased complications for mother and child during pregnancy and during and after delivery.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>STUDY FUNDING\/COMPETING INTEREST(S)<\/jats:title>\n                    <jats:p>The contribution of CM was partially supported by the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant No 681546, FAMSIZEMATTERS), Nuffield College, and the Leverhulme Trust. The contribution of GP was partially supported by the French Agence Nationale de la Recherche (grant No ANR-18-CE36-0007-07). The authors declare no conflict of interest.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>TRIAL REGISTRATION NUMBER<\/jats:title>\n                    <jats:p>N\/A.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1093\/humrep\/deab029","type":"journal-article","created":{"date-parts":[[2021,1,28]],"date-time":"2021-01-28T16:16:22Z","timestamp":1611850582000},"page":"1666-1673","source":"Crossref","is-referenced-by-count":209,"title":["Twin Peaks: more twinning in humans than ever before"],"prefix":"10.1093","volume":"36","author":[{"given":"Christiaan","family":"Monden","sequence":"first","affiliation":[{"name":"University of Oxford, OX1 2JD Oxford, UK"},{"name":"Nuffield College, OX1 1NF Oxford, UK"},{"name":"Leverhulme Centre for Demographic Science, OX1 1JD Oxford, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gilles","family":"Pison","sequence":"additional","affiliation":[{"name":"French Institute for Demographic Studies (INED), 75980 Paris, France"},{"name":"French Museum of Natural History (UMR 7206), 75005 Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeroen","family":"Smits","sequence":"additional","affiliation":[{"name":"Global Data Lab, Institute for Management Research, Radboud University, 6525 XZ Nijmegen, the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2021,3,12]]},"reference":[{"key":"2021051805592258800_deab029-B1","doi-asserted-by":"crossref","first-page":"377","DOI":"10.1530\/REP-08-0206","article-title":"Monozygotic twinning associated with assisted reproductive technologies: a review","volume":"136","author":"Aston","year":"2008","journal-title":"Reproduction"},{"key":"2021051805592258800_deab029-B2","doi-asserted-by":"crossref","first-page":"428","DOI":"10.1016\/j.ajog.2007.10.783","article-title":"Twin pregnancy and the risk of preeclampsia: bigger placenta or relative ischemia?","volume":"198","author":"Bdolah","year":"2008","journal-title":"Am J Obstet Gynecol"},{"key":"2021051805592258800_deab029-B3","doi-asserted-by":"crossref","first-page":"1531","DOI":"10.1093\/humrep\/del009","article-title":"The paradox of declining fertility but increasing twinning rates with advancing maternal age","volume":"21","author":"Beemsterboer","year":"2006","journal-title":"Hum Reprod"},{"key":"2021051805592258800_deab029-B4","doi-asserted-by":"crossref","first-page":"239","DOI":"10.1053\/sper.2002.34775","article-title":"Trends in the occurrence, determinants, and consequences of multiple births","volume":"26","author":"Blondel","year":"2002","journal-title":"Semin Perinatol"},{"key":"2021051805592258800_deab029-B5","doi-asserted-by":"crossref","first-page":"179","DOI":"10.1093\/humupd\/5.2.179","article-title":"The epidemiology of multiple births","volume":"5","author":"Bortolus","year":"1999","journal-title":"Hum Reprod Update"},{"key":"2021051805592258800_deab029-B6","doi-asserted-by":"crossref","first-page":"hoy003","DOI":"10.1093\/hropen\/hoy003","article-title":"Availability, effectiveness and safety of ART in sub-Saharan Africa: a systematic review","volume":"2018","author":"Botha","year":"2018","journal-title":"Hum Reprod Open"},{"key":"2021051805592258800_deab029-B7","volume-title":"The Biology of Twinning in Man","author":"Bulmer","year":"1970"},{"key":"2021051805592258800_deab029-B8","doi-asserted-by":"crossref","first-page":"1147","DOI":"10.1542\/peds.2008-1619","article-title":"Multiple births are a risk factor for postpartum maternal depressive symptoms'","volume":"123","author":"Choi","year":"2009","journal-title":"Pediatrics"},{"key":"2021051805592258800_deab029-B9","doi-asserted-by":"crossref","first-page":"265","DOI":"10.1093\/humupd\/8.3.265","article-title":"An international survey of the health economics of IVF and ICSI'","volume":"8","author":"Collins","year":"2002","journal-title":"Hum Reprod Update"},{"key":"2021051805592258800_deab029-B10","doi-asserted-by":"crossref","first-page":"1485","DOI":"10.1542\/peds.2008-1216","article-title":"Behavioral problems and cognitive performance at 5 years of age after very preterm birth: the EPIPAGE Study","volume":"123","author":"Delobel-Ayoub","year":"2009","journal-title":"Pediatrics"},{"key":"2021051805592258800_deab029-B11","doi-asserted-by":"crossref","first-page":"e0209962","DOI":"10.1371\/journal.pone.0209962","article-title":"Temporal trends in the birth rates and perinatal mortality of twins: apopulation-based study in China","volume":"14","author":"Deng","year":"2019","journal-title":"PLoS ONE"},{"key":"2021051805592258800_deab029-B12","doi-asserted-by":"crossref","first-page":"2247","DOI":"10.1093\/humrep\/der180","article-title":"Time trends in the natural dizygotic twinning rate'","volume":"26","author":"Derom","year":"2011","journal-title":"Hum Reprod"},{"key":"2021051805592258800_deab029-B13","first-page":"767","article-title":"On some laws of the production of twins","volume":"10","author":"Duncan","year":"1865","journal-title":"Edinb Med J"},{"key":"2021051805592258800_deab029-B14","doi-asserted-by":"crossref","first-page":"604","DOI":"10.1016\/j.rbmo.2020.06.021","article-title":"Assisted reproductive technology in Africa: a 5-year trend analysis from the African Network and Registry for ART","volume":"41","author":"Dyer","year":"2020","journal-title":"Reprod BioMed Online"},{"key":"2021051805592258800_deab029-B15","doi-asserted-by":"crossref","first-page":"192","DOI":"10.1126\/science.ns-20.504.192-b","article-title":"Twins among the Indians on puget sound","volume":"20","author":"Eells","year":"1892","journal-title":"Science"},{"key":"2021051805592258800_deab029-B16","first-page":"hoaa032","article-title":"ART in Europe, 2016: results generated from European registries by ESHRE'","author":"European IVF monitoring Consortium","year":"2020","journal-title":"Hum Reprod Open"},{"key":"2021051805592258800_deab029-B17","doi-asserted-by":"crossref","DOI":"10.1093\/hropen\/hox012","article-title":"Trends over 15 years in ART in Europe: an analysis of 6 million cycles","volume":"2017","author":"Ferraretti","year":"2017","journal-title":"Hum Reprod Open"},{"key":"2021051805592258800_deab029-B18","doi-asserted-by":"crossref","first-page":"56","DOI":"10.1017\/thg.2018.70","article-title":"Twinning rates in Uruguay between 1999 and 2015: association with socioeconomic and demographic factors","volume":"22","author":"G\u00f3mez","year":"2019","journal-title":"Twin Res Hum Genet"},{"key":"2021051805592258800_deab029-B19","doi-asserted-by":"crossref","first-page":"495","DOI":"10.1080\/0032472031000147266","article-title":"Child mortality among twins in less developed countries","volume":"47","author":"Guo","year":"1993","journal-title":"Popul Stud"},{"key":"2021051805592258800_deab029-B20","doi-asserted-by":"crossref","first-page":"735","DOI":"10.1016\/S0140-6736(03)14237-7","article-title":"Twinning","volume":"362","author":"Hall","year":"2003","journal-title":"The Lancet"},{"key":"2021051805592258800_deab029-B21","doi-asserted-by":"crossref","first-page":"37","DOI":"10.1093\/humupd\/dmm036","article-title":"Dizygotic twinning","volume":"14","author":"Hoekstra","year":"2008","journal-title":"Hum Reprod Update"},{"key":"2021051805592258800_deab029-B22","doi-asserted-by":"crossref","first-page":"209","DOI":"10.1017\/S0001566000000441","article-title":"Trends of twinning rates in ten countries, 1972\u20131996","volume":"46","author":"Imaizumi","year":"1997","journal-title":"Acta Genet Med Gemellol Twin Res"},{"key":"2021051805592258800_deab029-B23","doi-asserted-by":"crossref","first-page":"411","DOI":"10.1093\/humupd\/dmv016","article-title":"Infertility around the globe: new thinking on gender, reproductive technologies and global movements in the 21st century","volume":"21","author":"Inhorn","year":"2015","journal-title":"Hum Reprod Update"},{"key":"2021051805592258800_deab029-B24","doi-asserted-by":"crossref","first-page":"892","DOI":"10.1097\/AOG.0b013e3182102adf","article-title":"Association between the birth of twins and parental divorce","volume":"117","author":"Jena","year":"2011","journal-title":"Obstet Gynecol"},{"key":"2021051805592258800_deab029-B25","doi-asserted-by":"crossref","first-page":"F139","DOI":"10.1136\/adc.2002.020396","article-title":"Survival of very preterm infants: epipage, a population based cohort study","volume":"89","author":"Larroque","year":"2004","journal-title":"Arch Dis Child Fetal Neonatal Ed"},{"key":"2021051805592258800_deab029-B26","doi-asserted-by":"crossref","first-page":"549","DOI":"10.1016\/S0140-6736(00)40112-1","article-title":"Statistics of multiple births","volume":"35","author":"Mackenzie","year":"1841","journal-title":"The Lancet"},{"key":"2021051805592258800_deab029-B27","author":"Martin","year":"2012"},{"key":"2021051805592258800_deab029-B28","doi-asserted-by":"crossref","first-page":"258","DOI":"10.1002\/(SICI)1096-8628(19960122)61:3<258::AID-AJMG10>3.0.CO;2-S","article-title":"Genetic modelling of dizygotic twinning in pedigrees of spontaneous dizygotic twins","volume":"61","author":"Meulemans","year":"1996","journal-title":"Am J Med Genet"},{"key":"2021051805592258800_deab029-B29","volume-title":"Report to the European Union of the Collaborative Project","author":"Mills","year":"2014"},{"key":"2021051805592258800_deab029-B30","doi-asserted-by":"crossref","first-page":"e673","DOI":"10.1016\/S2214-109X(17)30197-3","article-title":"Mortality among twins and singletons in sub-Saharan Africa between 1995 and 2014: a pooled analysis of data from 90 Demographic and Health Surveys in 30 countries","volume":"5","author":"Monden","year":"2017","journal-title":"The Lancet Global Health"},{"key":"2021051805592258800_deab029-B31","first-page":"1513","article-title":"Results generated from European registers by ESHRE'","volume":"22","author":"Nyboer","year":"2007","journal-title":"Human Reproduction"},{"key":"2021051805592258800_deab029-B32","volume-title":"Mortality and Society in Sub-Saharan Africa","author":"Pison","year":"1992"},{"key":"2021051805592258800_deab029-B42","first-page":"1","article-title":"Nearly half of the world's twins are born in Africa","volume":"360","author":"Pison","year":"2000","journal-title":"Popul Soc"},{"key":"2021051805592258800_deab029-B33","doi-asserted-by":"crossref","first-page":"765","DOI":"10.2307\/3654937","article-title":"The frequency of twin births in France. The triple influence of biology, medicine and family behaviour","volume":"59","author":"Pison","year":"2004","journal-title":"Population"},{"key":"2021051805592258800_deab029-B34","doi-asserted-by":"crossref","first-page":"250","DOI":"10.1375\/twin.9.2.250","article-title":"Frequency of twin births in developed countries","volume":"9","author":"Pison","year":"2006","journal-title":"Twin Res Hum Genet"},{"key":"2021051805592258800_deab029-B35","doi-asserted-by":"crossref","first-page":"629","DOI":"10.1111\/j.1728-4457.2015.00088.x","article-title":"Twinning rates in developed countries: trends and explanations","volume":"41","author":"Pison","year":"2015","journal-title":"Popul Dev Rev"},{"key":"2021051805592258800_deab029-B36","doi-asserted-by":"crossref","first-page":"293","DOI":"10.1080\/14767050802663194","article-title":"Risk for developing gestational diabetes in women with twin pregnancies","volume":"22","author":"Rauh-Hain","year":"2009","journal-title":"J MaternFetal Neonatal Med"},{"key":"2021051805592258800_deab029-B37","volume-title":"Twin Mythconceptions: False Beliefs, Fables, and Facts about Twins","author":"Segal","year":"2017"},{"key":"2021051805592258800_deab029-B38","doi-asserted-by":"crossref","first-page":"1361","DOI":"10.1093\/humrep\/deq057","article-title":"Cross border reproductive care in six European countries","volume":"25","author":"Shenfield","year":"2010","journal-title":"Hum Reprod"},{"key":"2021051805592258800_deab029-B39","first-page":"6","author":"Smits","year":"2011"},{"key":"2021051805592258800_deab029-B40","author":"United Nations. Department of Economic and Social Affairs Population Division","year":"2017"},{"key":"2021051805592258800_deab029-B41","doi-asserted-by":"crossref","first-page":"262","DOI":"10.1126\/science.53.1368.262","article-title":"The relative numbers of twins and triplets","volume":"53","author":"Zeleny","year":"1921","journal-title":"Science"}],"container-title":["Human Reproduction"],"original-title":[],"language":"en","link":[{"URL":"http:\/\/academic.oup.com\/humrep\/article-pdf\/36\/6\/1666\/37948231\/deab029.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"http:\/\/academic.oup.com\/humrep\/article-pdf\/36\/6\/1666\/37948231\/deab029.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2021,5,18]],"date-time":"2021-05-18T02:02:26Z","timestamp":1621303346000},"score":1,"resource":{"primary":{"URL":"https:\/\/academic.oup.com\/humrep\/article\/36\/6\/1666\/6168658"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,3,12]]},"references-count":42,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2021,3,12]]},"published-print":{"date-parts":[[2021,5,17]]}},"URL":"https:\/\/doi.org\/10.1093\/humrep\/deab029","relation":{},"ISSN":["0268-1161","1460-2350"],"issn-type":[{"value":"0268-1161","type":"print"},{"value":"1460-2350","type":"electronic"}],"subject":[],"published-other":{"date-parts":[[2021,6,1]]},"published":{"date-parts":[[2021,3,12]]}}}