title: Length of day during early gestation as a predictor of risk for severe retinopathy of prematurity.
abstract: OBJECTIVE
  Fetal mice require light exposure in utero during early gestation for normal vascular development in the eye. Because angiogenic abnormalities in retinopathy of prematurity (ROP) are manifested in preterm infants, we investigated whether day length during early gestation was associated with severe ROP (SROP).
  
  
  METHODS
  Single-center, retrospective cohort study.
  
  
  METHODS
  We included a total of 343 premature infants (401-1250 g birth weight [BW], from 1998-2002): 684 eyes (1 eye each of 2 patients excluded) with 76 eyes developing SROP, defined as (1) classic threshold ROP in zone I or II, (2) type 1 ROP in zone I, or (3) in a few eyes, type 1 ROP in posterior zone II that was treated.
  
  
  METHODS
  For each infant, average day length (ADL) was calculated during different cumulative time periods and time windows after the estimated date of conception (EDC). Multiple logistic regression analysis (with generalized estimating equations to account for inter-eye correlation) was performed.
  
  
  METHODS
  Association of ADL during early gestation with SROP.
  
  
  RESULTS
  In a model evaluating all 684 eyes with 76 eyes developing SROP, BW, gestational age, multiple births, race, per capita income in the mother's residence ZIP code, and ADL during the first 90 days after the EDC were factors associated with the development of SROP. Each additional hour of ADL (90 days) decreased the likelihood of SROP by 28% (P = 0.015; odds ratio [OR], 0.72; 95% confidence interval [CI], 0.55-0.94). In a model evaluating the subset of 146 prethreshold ROP eyes with 76 eyes developing SROP, each additional hour of ADL during the first 105 days after the EDC decreased the likelihood of SROP by 46% (P = 0.001; OR, 0.54; 95% CI, 0.37-0.78). Time windows when ADL was most closely associated with SROP were 31 to 60 days and 61 to 90 days after the EDC for the all eyes and the prethreshold ROP eyes models, respectively.
  
  
  CONCLUSIONS
  Higher ADL during early gestation was associated with a lower risk for SROP and may imply a role for prophylactic light treatment during early gestation to decrease the risk of SROP.
authors.affiliation: Abrahamson Pediatric Eye Institute and the Visual Systems Group of the Division of Pediatric Ophthalmology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Department of Ophthalmology, University of Cincinnati, College of Medicine, Cincinnati, Ohio. Electronic address: Michael.Yang@cchmc.org.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Yang
authors.affiliation: Abrahamson Pediatric Eye Institute and the Visual Systems Group of the Division of Pediatric Ophthalmology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.
authors.forename: Sujata
authors.initials: S
authors.lastname: Rao
authors.affiliation: Departments of Ophthalmology and Physiology, University of California, San Francisco, San Francisco, California.
authors.forename: David R
authors.initials: DR
authors.lastname: Copenhagen
authors.affiliation: Abrahamson Pediatric Eye Institute and the Visual Systems Group of the Division of Pediatric Ophthalmology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Department of Ophthalmology, University of Cincinnati, College of Medicine, Cincinnati, Ohio; Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Lang
mesh_terms: D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D019102:Infant, Very Low Birth Weight; D008297:Male; D010298:Parity; D017440:Photoperiod; D011247:Pregnancy; D012178:Retinopathy of Prematurity / Q000209:etiology*; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D013997:Time Factors