title: Fetal and neonatal mortality among twin gestations in the United States: the role of intrapair birth weight discordance.
abstract: OBJECTIVE
  To examine the association of intrapair birth weight discordance with fetal and neonatal mortality.
  
  
  METHODS
  We used the United States (1995-1997) Matched Multiple Birth File (n = 297,155).
  
  
  RESULTS
  Among twin live births and stillborn fetuses, 29.9% had less than 5% birth weight discordance, 24.2% had 5-9%, 29.6% had 10-19%, 11.1% had 20-29%, 3.4% had 30-39%, and 1.8% had 40% or more. The stillborn fetus rate increased progressively with increasing birth weight discordance for smaller and larger twins of the same sex. Compared with the less than 5% birth weight discordance category, the adjusted odds ratios (OR) (95% confidence intervals [CIs]) for stillborn fetus associated with 5-9%, 10-19%, 20-29%, 30-39%, and 40% or more birth weight discordance, respectively, were 0.81 (95% CI 0.58, 1.11), 1.41 (95% CI 1.07, 1.84), 1.74 (95% CI 1.28, 2.35), 3.06 (95% CI 2.21, 4.24), and 4.29 (95% CI 3.05, 6.04) for smaller twins. The corresponding ORs (95% CIs) for larger twins were 0.78 (95% CI 0.57, 1.08), 1.26 (95% CI 0.96, 1.66), 1.77 (95% CI 1.27, 2.46), 3.38 (95% CI 2.33, 4.92), and 2.91 (95% CI 1.89, 4.47). Similar associations were observed among smaller but not larger twins of opposite sex. Among larger but not smaller twins of the same sex, increasing birth weight discordance was associated with overall neonatal deaths. This association was not apparent among smaller and larger twins of opposite sex. However, increasing birth weight discordance was associated with neonatal deaths related to congenital malformations among smaller and larger twins.
  
  
  CONCLUSIONS
  The results provide evidence that increased twin birth weight discordance was associated with increased risk of intrauterine death and malformation-related neonatal deaths.
authors.affiliation: Division of Epidemiology, School of Public Health, University of Medicine and Dentistry of New Jersey, Piscataway 08854, USA. demisski@umdnj.edu
authors.forename: Kitaw
authors.initials: K
authors.lastname: Demissie
authors.forename: Cande V
authors.initials: CV
authors.lastname: Ananth
authors.forename: Joyce
authors.initials: J
authors.lastname: Martin
authors.forename: Maryellen L
authors.initials: ML
authors.lastname: Hanley
authors.forename: Marian F
authors.initials: MF
authors.lastname: MacDorman
authors.forename: George G
authors.initials: GG
authors.lastname: Rhoads
mesh_terms: D000293:Adolescent; D000328:Adult; D001722:Birth Order; D001724:Birth Weight; D016001:Confidence Intervals; D005260:Female; D005313:Fetal Death; D005317:Fetal Growth Retardation / Q000175:diagnosis / Q000453:epidemiology*; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality / Q000639:trends*; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D016017:Odds Ratio; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D015995:Prevalence; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D014427:Twins; D014481:United States / Q000453:epidemiology