title: A new approach to estimating weight change and its reference intervals during the first 96 hours of life.
abstract: OBJECTIVE
  We aimed to apply a novel model to estimate weight change and its reference intervals during the first 96 h of life and the time of weight nadir.
  
  
  METHODS
  This study involved 1288 full-term singletons, from the Generation XXI birth cohort. Recruitment occurred between 2005 and 2006 in all five public units providing obstetrical and neonatal care in Porto, Portugal. Birthweight was abstracted from clinical records, and the subsequent newborn anthropometrics were obtained by trained examiners. Longitudinal models to estimate postnatal weight were tested and the weight ratio was calculated as the weight during 96 h of life divided by birthweight.
  
  
  RESULTS
  The chosen model was (weight(t)~ 3241.442 + (-9.378) × t + 0.119 × t(2) + 0.000 × t(3) + b0i + b1i × t, where t represented the newborn infant's age in hours and bi represented the random coefficients. The curve inflection point (nadir) was achieved at 52.3 h of life, corresponding to a loss of 218 g and a weight ratio of 0.933. We estimated that at six, 12, 24 and 36 h of life the mean weight ratio and 10th-90th percentiles were 0.978 (0.968-0.988), 0.968 (0.953-0.983), 0.951 (0.928-0.974) and 0.939 (0.909-0.969), respectively.
  
  
  CONCLUSIONS
  This model allows a more accurate estimate of newborn weight change and its reference intervals, and estimated the nadir at 52.3 h of life, corresponding to a weight ratio of 0.933.
authors.affiliation: EPIUnit - Institute of Public Health, University of Porto, Porto, Portugal.|Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal.
authors.forename: M J
authors.initials: MJ
authors.lastname: Fonseca
authors.affiliation: EPIUnit - Institute of Public Health, University of Porto, Porto, Portugal.|Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal.
authors.forename: M
authors.initials: M
authors.lastname: Severo
authors.affiliation: EPIUnit - Institute of Public Health, University of Porto, Porto, Portugal.|Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal.
authors.forename: A C
authors.initials: AC
authors.lastname: Santos
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D057238:Growth Charts; D006801:Humans; D007231:Infant, Newborn / Q000254:growth & development*; D008297:Male; D011247:Pregnancy; D012016:Reference Values; D015431:Weight Loss; D055815:Young Adult
keywords: neonate; newborn; reference intervals; weight loss