{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,3]],"date-time":"2026-06-03T12:02:28Z","timestamp":1780488148606,"version":"3.54.1"},"reference-count":34,"publisher":"Wiley","issue":"3","license":[{"start":{"date-parts":[[2021,9,1]],"date-time":"2021-09-01T00:00:00Z","timestamp":1630454400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["obgyn.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Ultrasound in Obstet &amp; Gyne"],"published-print":{"date-parts":[[2021,9]]},"abstract":"<jats:title>ABSTRACT<\/jats:title><jats:sec><jats:title>Objectives<\/jats:title><jats:p>To construct chorionicity\u2010specific birth\u2010weight reference charts for dichorionic diamniotic (DCDA) and monochorionic diamniotic (MCDA) twin pregnancies, incorporating estimated\u2010fetal\u2010weight (EFW) data in order to adjust for the relationship between suboptimal growth and preterm delivery. An additional aim was to determine if the inclusion of complicated twin pregnancies impacts on the reference charts produced.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>The inclusion criteria for this retrospective cohort study were twin pregnancy of known DCDA or MCDA chorionicity, known pregnancy outcome, last ultrasound scan within 14\u2009days before  birth and delivery between 25 and 38\u2009weeks' gestation (Analysis A). An analysis was also conducted excluding pregnancies with complications recorded (Analysis B). Previously published twin EFW reference ranges were used in the analysis. A joint statistical model for EFW and observed birth weight for each pregnancy was created in order to estimate population birth\u2010weight reference ranges corresponding to the distribution expected if all pregnancies delivered at any given gestational age. It was not assumed that the median EFW was equal to birth weight for any given gestational age. The models were fitted using a Bayesian approach.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>We retrieved data on 1664 twin pregnancies, of which 707 DCDA and 241 MCDA pregnancies met the inclusion criteria. In Analysis A, the estimated population median birth weight was similar to the median EFW at around 27\u2009weeks' gestation but fell below the EFW values with increasing gestation, being 156\u2009g lower in both DCDA and MCDA pregnancies at 35\u2009weeks; this finding was confirmed by direct comparison of the last EFW and birth\u2010weight values in each pregnancy. When the analysis was repeated after excluding complicated twin pregnancies (Analysis B), compared with Analysis A, there was very little difference in the median birth\u2010weight results obtained across gestation. The largest absolute difference between Analyses A and B for DCDA twins was at 31, 32 and 33\u2009weeks, with a 9\u2010g lower median birth weight in Analysis A compared with Analysis B. The largest absolute difference for MCDA twins was greater than that for DCDA twins, with a 21\u2010g lower median birth weight at 25\u2009weeks in Analysis A compared with Analysis B.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>We have established population chorionicity\u2010specific birth\u2010weight reference charts for DCDA and MCDA twin pregnancies, corresponding to the range expected were all pregnancies  to deliver at any given gestational age. In this population of twins, the median birth weight was consistently lower than that reported for singletons, and there was variation in the median birth weight at different gestational ages according to chorionicity. \u00a9 2021 The Authors. Ultrasound in Obstetrics &amp; Gynecology published by John Wiley &amp; Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.\n\u2010 Legal Statement: This is an open access article under the terms of the Creative Commons Attribution\u2010NonCommercial\u2010NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non\u2010commercial and no modifications or adaptations are made.<\/jats:p><\/jats:sec>","DOI":"10.1002\/uog.23606","type":"journal-article","created":{"date-parts":[[2021,2,6]],"date-time":"2021-02-06T04:27:23Z","timestamp":1612585643000},"page":"439-449","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":24,"title":["Twin chorionicity\u2010specific population birth\u2010weight charts adjusted for estimated fetal weight"],"prefix":"10.1002","volume":"58","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1508-3473","authenticated-orcid":false,"given":"C.","family":"Briffa","sequence":"first","affiliation":[{"name":"Twins Trust Centre for Research and Clinical Excellence St George's University Hospitals NHS Foundation Trust  London UK"},{"name":"Vascular Biology Research Centre Molecular and Clinical Sciences Research Institute, St George's University of London  London UK"},{"name":"Fetal Medicine Unit St George's University Hospitals NHS Foundation Trust  University of London, London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"O.","family":"Stirrup","sequence":"additional","affiliation":[{"name":"Institute for Global Health University College London  London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"C.","family":"Huddy","sequence":"additional","affiliation":[{"name":"Twins Trust Centre for Research and Clinical Excellence St George's University Hospitals NHS Foundation Trust  London UK"},{"name":"Neonatal Unit St George's University Hospitals NHS Foundation Trust  London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"J.","family":"Richards","sequence":"additional","affiliation":[{"name":"Twins Trust Centre for Research and Clinical Excellence St George's University Hospitals NHS Foundation Trust  London UK"},{"name":"Neonatal Unit St George's University Hospitals NHS Foundation Trust  London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"S.","family":"Shetty","sequence":"additional","affiliation":[{"name":"Twins Trust Centre for Research and Clinical Excellence St George's University Hospitals NHS Foundation Trust  London UK"},{"name":"Neonatal Unit St George's University Hospitals NHS Foundation Trust  London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"K.","family":"Reed","sequence":"additional","affiliation":[{"name":"Twins Trust  Aldershot UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2802-7670","authenticated-orcid":false,"given":"A.","family":"Khalil","sequence":"additional","affiliation":[{"name":"Twins Trust Centre for Research and Clinical Excellence St George's University Hospitals NHS Foundation Trust  London UK"},{"name":"Vascular Biology Research Centre Molecular and Clinical Sciences Research Institute, St George's University of London  London UK"},{"name":"Fetal Medicine Unit St George's University Hospitals NHS Foundation Trust  University of London, London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2021,9]]},"reference":[{"key":"e_1_2_7_2_1","unstructured":"Office for National Statistics.Birth characteristics in England and Wales: 2018. 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