title: A co-twin study of the relative effect of birth weight and gestational age on retinopathy of prematurity.
abstract: OBJECTIVE
  To determine the relative effect of birth weight and gestational age on retinopathy of prematurity (ROP) using preterm twin pairs discordant for birth weight.
  
  
  METHODS
  This study was a retrospective cohort study including 55 consecutive twin pairs of 110 preterm infants (gestational age ≤33 weeks). The outcomes of ROP including occurrence (any stage), severe ROP (stage 3 or more), and clinically significant ROP requiring laser treatment were compared between twins with the lower birth weight from each pair and their co-twins with the higher birth weight. Using twin pairs having different birth weight and identical gestational age, the independent effects of prematurity and intrauterine growth on ROP could be evaluated. Other perinatal morbidities related to prematurity were also compared between twin pairs.
  
  
  RESULTS
  No significant differences in ROP between larger and smaller infants were observed in the twin-paired analysis while analysis on individual infants showed strong association between small birth weight and ROP outcomes. However, in both the larger and smaller infant groups, gestational age of <28 weeks was significantly associated with ROP outcomes. No differences were found between twin pairs regarding other perinatal morbidities including bronchopulmonary dysplasia, respiratory distress syndrome, patent ductus arteriosus, intraventricular hemorrhage, and periventricular leukomalacia.
  
  
  CONCLUSIONS
  Birth weight is not associated with ROP, while gestational age is in the twin-paired study, suggesting that gestational age is a better predictor of ROP than birth weight. This indicates that maturity is more important in the pathogenesis of ROP than intrauterine growth.
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: S J
authors.initials: SJ
authors.lastname: Woo
authors.forename: K H
authors.initials: KH
authors.lastname: Park
authors.forename: J
authors.initials: J
authors.lastname: Ahn
authors.forename: K J
authors.initials: KJ
authors.lastname: Oh
authors.forename: S Y
authors.initials: SY
authors.lastname: Lee
authors.forename: E H
authors.initials: EH
authors.lastname: Jeong
authors.forename: K H
authors.initials: KH
authors.lastname: Park
mesh_terms: D001724:Birth Weight; D015331:Cohort Studies; D004200:Diseases in Twins / Q000453:epidemiology* / Q000473:pathology; D005260:Female; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007234:Infant, Premature; D007723:Korea / Q000453:epidemiology; D008297:Male; D012178:Retinopathy of Prematurity / Q000453:epidemiology* / Q000473:pathology; D012189:Retrospective Studies; D012307:Risk Factors; D014427:Twins