{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,8]],"date-time":"2026-10-08T13:31:31Z","timestamp":1791466291178,"version":"4.3.4"},"reference-count":32,"publisher":"Oxford University Press (OUP)","issue":"5","license":[{"start":{"date-parts":[[2021,11,29]],"date-time":"2021-11-29T00:00:00Z","timestamp":1638144000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Health and Medical Research Council\u2019s (NHMRC) Australian Centre of Excellence in Twin Research","award":["APP1079102"],"award-info":[{"award-number":["APP1079102"]}]},{"name":"Newton International Fellow Alumnus (Royal Society"},{"DOI":"10.13039\/501100000925","name":"NHMRC","doi-asserted-by":"publisher","award":["APP1193838"],"award-info":[{"award-number":["APP1193838"]}],"id":[{"id":"10.13039\/501100000925","id-type":"DOI","asserted-by":"publisher"}]},{"name":"NHMRC Senior Principal Research Fellow","award":["APP1137349"],"award-info":[{"award-number":["APP1137349"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2022,10,13]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:sec>\n                  <jats:title>Background<\/jats:title>\n                  <jats:p>In infancy, males are at higher risk of dying than females. Birthweight and gestational age are potential confounders or mediators but are also familial and correlated, posing epidemiological challenges that can be addressed by studying male-female twin pairs.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>We studied 28\u00a0558 male-female twin pairs born in Brazil between 2012 and 2016, by linking their birth and death records. Using a co-twin control study matched for gestational age and familial factors, we applied logistic regression with random effects (to account for paired data) to study the association between male sex and infant death, adjusting for: birthweight, within- and between-pair effects of birthweight, birth order and gestational age, including interactions. The main outcome was infant mortality (0\u2013365\u2009days) stratified by neonatal (early and late) and postneonatal deaths.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Males were 100\u2009g heavier and more at risk of infant death than their female co-twins before [odds ratio (OR) \u2009=\u20091.28, 95% confidence interval (CI): 1.11\u20131.49, P\u2009=\u20090.001] and after (OR\u2009=\u20091.60, 95% CI: 1.39\u20131.83, P\u2009&amp;lt;0.001) adjusting for birthweight and birth order. When adjusting for birthweight within-pair difference and mean separately, the OR attenuated to 1.40 (95% CI: 1.21\u20131.61, P\u2009&amp;lt;0.001), with evidence of familial confounding (likelihood ratio test, P\u2009&amp;lt;0.001). We found evidence of interaction (P\u2009=\u20090.001) between male sex and gestational age for early neonatal death.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>After matching for gestational age and familial factors by design and controlling for birthweight and birth order, males remain at greater risk of infant death than their female co-twins. Birthweight\u2019s role as a confounder can be partially explained by familial factors.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1093\/ije\/dyab242","type":"journal-article","created":{"date-parts":[[2021,11,5]],"date-time":"2021-11-05T12:18:46Z","timestamp":1636114726000},"page":"1502-1510","source":"Crossref","is-referenced-by-count":14,"title":["Birthweight, gestational age and familial confounding in sex differences in infant mortality: a matched co-twin control study of Brazilian male-female twin pairs identified by population data linkage"],"prefix":"10.1093","volume":"51","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6153-8080","authenticated-orcid":false,"given":"Lucas","family":"Calais-Ferreira","sequence":"first","affiliation":[{"name":"Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne , Melbourne, VIC, Australia"},{"name":"Centre for Adolescent Health, Murdoch Children\u2019s Research Institute , Melbourne, VIC, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marcos E","family":"Barreto","sequence":"additional","affiliation":[{"name":"AtyImoLab, Computer Science Department, Federal University of Bahia , Salvador, Brazil"},{"name":"Department of Statistics, London School of Economics and Political Science , London, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Everton","family":"Mendon\u00e7a","sequence":"additional","affiliation":[{"name":"AtyImoLab, Computer Science Department, Federal University of Bahia , Salvador, Brazil"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2448-2548","authenticated-orcid":false,"given":"Gillian S","family":"Dite","sequence":"additional","affiliation":[{"name":"Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne , Melbourne, VIC, Australia"},{"name":"Genetic Technologies Ltd. , Melbourne, VIC, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3941-082X","authenticated-orcid":false,"given":"Martha","family":"Hickey","sequence":"additional","affiliation":[{"name":"Royal Women\u2019s Hospital , Melbourne, VIC, Australia"},{"name":"Department of Obstetrics and Gynaecology, University of Melbourne , Melbourne, VIC, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Paulo H","family":"Ferreira","sequence":"additional","affiliation":[{"name":"Charles Perkins Centre Musculoskeletal Hub, Faculty of Medicine and Health, University of Sydney , Sydney, NSW, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5226-7370","authenticated-orcid":false,"given":"Katrina J","family":"Scurrah","sequence":"additional","affiliation":[{"name":"Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne , Melbourne, VIC, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"John L","family":"Hopper","sequence":"additional","affiliation":[{"name":"Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne , Melbourne, VIC, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2021,11,29]]},"reference":[{"key":"2022101309184100600_dyab242-B1","author":"UNICEF","year":"2020"},{"key":"2022101309184100600_dyab242-B2","doi-asserted-by":"crossref","first-page":"902","DOI":"10.1542\/peds.48.6.902","article-title":"Neonatal mortality, the male disadvantage","volume":"48","author":"Naeye","year":"1971","journal-title":"Pediatrics"},{"key":"2022101309184100600_dyab242-B3","doi-asserted-by":"crossref","first-page":"303","DOI":"10.1016\/j.jmhg.2004.09.010","article-title":"Sex and gender differences in newborn infants: why are boys at increased 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