title: Birth weight references for twins.
abstract: OBJECTIVE
  We sought to formulate fetal and birth weight references for twins from longitudinal data.
  
  
  METHODS
  This historic cohort study was based on 1831 pregnancies of twins born alive at >/=28 weeks' gestation from Baltimore, Maryland; Miami, Florida; Charleston, South Carolina; and Ann Arbor, Michigan.
  
  
  RESULTS
  When we compared singletons and twins, the percentiles of twins fell substantially below the 10th percentile of singletons by 28 weeks' gestation, below the 50th percentile by 30 weeks' gestation, and below the 90th percentile by 34 weeks' gestation. The difference at the 50th percentile was 147 g (10%) at 30 weeks' gestation, 242 g (14%) at 32 weeks' gestation, 347 g (17%) at 34 weeks' gestation, 450 g (19%) at 36 weeks' gestation, 579 g (22%) at 38 weeks' gestation, and 772 g (27%) at 40 weeks' gestation.
  
  
  CONCLUSIONS
  This new reference demonstrates that, although the overall pattern of fetal growth is slower for twins versus singletons from about 30 weeks' gestation, well-grown twins and singletons do not differ as much as previously believed.
authors.affiliation: Center for Statistical Consultation and Research, University of Michigan, Ann Arbor 48109-0264, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Min
authors.forename: B
authors.initials: B
authors.lastname: Luke
authors.forename: B
authors.initials: B
authors.lastname: Gillespie
authors.forename: L
authors.initials: L
authors.lastname: Min
authors.forename: R B
authors.initials: RB
authors.lastname: Newman
authors.forename: J G
authors.initials: JG
authors.lastname: Mauldin
authors.forename: F R
authors.initials: FR
authors.lastname: Witter
authors.forename: F A
authors.initials: FA
authors.lastname: Salman
authors.forename: M J
authors.initials: MJ
authors.lastname: O'sullivan
mesh_terms: D000328:Adult; D001724:Birth Weight; D001835:Body Weight; D005314:Embryonic and Fetal Development; D005260:Female; D020567:Fetal Weight; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007246:Infertility / Q000628:therapy; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D012016:Reference Values; D012907:Smoking; D016216:Ultrasonography, Prenatal