title: Risk factors for intrapair birth weight discordance in twins.
abstract: OBJECTIVE
  To determine the risk factors for birth weight discordance in twins.
  
  
  METHODS
  We used the United States (1995-97) Matched Multiple Birth File (n = 294 568) to assess the association between birth weight discordance and maternal sociodemographic, pregnancy and infant characteristics.
  
  
  RESULTS
  Eighty-four per cent of the twins were 0-19% discordant, 11.1% were 20-29% discordant, 3.4% were 30-39% discordant, and 1.8% were > or = 2 40% discordant. The risk factors for birth weight discordance for same-sex twins were eclampsia (odds ratio (OR) 1.39,95% confidence interval (CI) 1.20, 1.61), pre-eclampsia (OR 1.31, 95% CI 1.24, 1.38), pre-existing hypertension (OR 1.32, 95% CI 1.12, 1.56), diabetes (OR 1.13, 95% CI 1.04, 1.24) and certain congenital anomalies. For opposite-sex twins, the risk factors for birth weight discordance were pre-eclampsia (OR 1.17, 95% CI 1.09, 1.27), pre-existing hypertension (OR 1.59,95% CI 1.32, 1.91), and certain congenital anomalies. Also, smoking and increased maternal age were associated with birth weight discordance in both same-sex and opposite-sex twins.
  
  
  CONCLUSIONS
  Maternal hypertensive disorders, smoking and delayed childbearing were associated with intrapair birth weight discordance. The mechanisms of these associations deserve further investigation.
authors.affiliation: Division of Epidemiology, University of Medicine and Dentistry of New Jersey, School of Public Health, Piscataway, New Jersey 08854, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sannoh
authors.forename: K
authors.initials: K
authors.lastname: Demissie
authors.forename: B
authors.initials: B
authors.lastname: Balasubramanian
authors.forename: G G
authors.initials: GG
authors.lastname: Rhoads
mesh_terms: D000293:Adolescent; D000328:Adult; D001724:Birth Weight; D000013:Congenital Abnormalities; D004200:Diseases in Twins / Q000453:epidemiology*; D004461:Eclampsia / Q000150:complications; D005260:Female; D005865:Gestational Age; D006801:Humans; D006973:Hypertension / Q000150:complications; D008297:Male; D008423:Maternal Age; D016017:Odds Ratio; D011225:Pre-Eclampsia / Q000150:complications; D011247:Pregnancy; D011248:Pregnancy Complications; D011253:Pregnancy in Adolescence; D011254:Pregnancy in Diabetics / Q000150:complications; D018566:Pregnancy, High-Risk; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking