title: Low birth weight is a risk factor for severe retinopathy of prematurity depending on gestational age.
abstract: OBJECTIVE
  To evaluate the impact of low birth weight as a risk factor for retinopathy of prematurity (ROP) that will require treatment in correlation with gestational age at birth (GA).
  
  
  METHODS
  In total, 2941 infants born <32 weeks GA were eligible from five cohorts of preterm infants previously collected for analysis in WINROP (Weight IGF-I Neonatal ROP) from the following locations: Sweden (EXPRESS) (n = 426), North America (n = 1772), Boston (n = 338), Lund (n = 52), and Gothenburg (n = 353). Data regarding GA at birth, birth weight (BW), gender, and need for ROP treatment were retrieved. Birth weight standard deviation scores (BWSDS) were calculated with Swedish as well as Canadian reference models. Small for gestational age (SGA) was defined as BWSDS less than -2.0 SDS using the Swedish reference and as BW below the 10th percentile using the Canadian reference charts.
  
  
  RESULTS
  Univariate analysis showed that low GA (p<0.001), low BW (p<0.001), male gender (p<0.05), low BWSDSCanada (p<0.001), and SGACanada (p<0.01) were risk factors for ROP that will require treatment. In multivariable logistic regression analysis, low GA (p<0.0001), male gender (p<0.01 and p<0.05), and an interaction term of BWSDS*GA group (p<0.001), regardless of reference chart, were risk factors. Low BWSDS was less important as a risk factor in infants born at GA <26 weeks compared with infants born at GA ≥26 weeks calculated with both reference charts (BWSDSSweden, OR = 0.80 vs 0.56; and BWSDSCanada, OR = 0.72 vs 0.41).
  
  
  CONCLUSIONS
  Low BWSDS as a risk factor for vision-threatening ROP is dependent on the infant's degree of immaturity. In more mature infants (GA ≥26 weeks), low BWSDS becomes a major risk factor for developing ROP that will require treatment. These results persist even when calculating BW deficit with different well-established approaches.
authors.affiliation: Institute of Neuroscience and Physiology, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.
authors.forename: Pia
authors.initials: P
authors.lastname: Lundgren
authors.affiliation: Institute of Neuroscience and Physiology, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden; Institution of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Kistner
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Andersson
authors.affiliation: Department of Pediatrics, Institute of Clinical Sciences, Lund University and Skane University Hospital, Lund, Sweden.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Hansen Pupp
authors.affiliation: Department of Neuroscience, Ophthalmology, Uppsala University, Uppsala, Sweden.
authors.forename: Gerd
authors.initials: G
authors.lastname: Holmström
authors.affiliation: Department of Pediatrics, Institute of Clinical Sciences, Lund University and Skane University Hospital, Lund, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Ley
authors.affiliation: Department of Pediatrics, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.
authors.forename: Aimon
authors.initials: A
authors.lastname: Niklasson
authors.affiliation: Department of Ophthalmology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Lois E H
authors.initials: LE
authors.lastname: Smith
authors.affiliation: Department of Ophthalmology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Carolyn
authors.initials: C
authors.lastname: Wu
authors.affiliation: Institute of Neuroscience and Physiology, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.
authors.forename: Ann
authors.initials: A
authors.lastname: Hellström
authors.affiliation: Institute of Neuroscience and Physiology, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.
authors.forename: Chatarina
authors.initials: C
authors.lastname: Löfqvist
mesh_terms: D002170:Canada; D005260:Female; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D012178:Retinopathy of Prematurity / Q000453:epidemiology / Q000473:pathology*; D012307:Risk Factors; D013548:Sweden; D047929:Term Birth