title: The distribution of intra-twin birth weight discordance and its association with total twin birth weight, gestational age, and neonatal mortality.
abstract: OBJECTIVE
  To determine an appropriate cutoff value to differentiate physiologic and pathologic birth weight discordance, to determine the prevalence of birth weight discordance > or =25% among twin pregnancies in different sub-populations, and to examine its clinical significance.
  
  
  METHODS
  Historical cohort study of 147,262 twin sets registered in the United States between 1995 and 1997.
  
  
  RESULTS
  The prevalence of birth weight discordance > or =25% among twin pregnancies was 8.6%. The prevalence of birth weight discordance > or =25% was significantly decreased with increasing total twin birth weight deciles, was more frequently found in twins with discordant gender (9.1%) than in those twins with concordant gender (8.3%) and in mothers whose age was 30 years or older (9.1%) than those of younger mothers (8.1%). Birth weight discordance > or =25% was associated with earlier gestational age at delivery (35.0 weeks versus 36.0 weeks) and higher neonatal mortality (5.4% versus 2.3%) as compared to twins with lower birth weight discordance.
  
  
  CONCLUSIONS
  The prevalence of birth weight discordance > or =25% among twin pregnancies was 8.6%, which is associated with lower gestational age at delivery and higher neonatal mortality rates, and may represent a pathologic process.
authors.affiliation: OMNI Research Group, Department of Obstetrics & Gynecology, Faculty of Medicine, University of Ottawa, Ont., Canada.
authors.forename: Hongzhuan
authors.initials: H
authors.lastname: Tan
authors.forename: Shi Wu
authors.initials: SW
authors.lastname: Wen
authors.forename: Karen
authors.initials: K
authors.lastname: Fung Kee Fung
authors.forename: Mark
authors.initials: M
authors.lastname: Walker
authors.forename: Kitaw
authors.initials: K
authors.lastname: Demissie
mesh_terms: D000328:Adult; D001724:Birth Weight; D015331:Cohort Studies; D016001:Confidence Intervals; D005260:Female; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D008423:Maternal Age; D016017:Odds Ratio; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011296:Prenatal Diagnosis; D012189:Retrospective Studies; D018570:Risk Assessment; D012737:Sex Factors; D014427:Twins