title: Comparison of US Birth Weight References and the International Fetal and Newborn Growth Consortium for the 21st Century Standard.
abstract: OBJECTIVE
  This study introduces how the International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st) international birth weight standards alter our previous understanding and interpretations of fetal growth restriction as represented by small for gestational age (SGA) status.
  
  
  OBJECTIVE
  To compare the birth weight distributions of the INTERGROWTH-21st international standard to commonly used US references and examine the differences in the prevalence and neonatal mortality risk of SGA status (below the 10th percentile of a population reference).
  
  
  METHODS
  We analyzed data from 16 prospective cohorts of newborns on gestational age, birth weight, and systematic mortality follow-up through 28 days from 10 low- and middle-income countries. The studies included were conducted between 1983 and 2008. The analysis was conducted in 2014. Infants were categorized as SGA using the 1991 US birth weight reference, the 1999-2000 US birth weight reference, and the new INTERGROWTH-21st standard. For each study, we compared the SGA prevalence and the risk ratio between SGA status and neonatal mortality, calculated using Poisson regression with robust error variance.
  
  
  METHODS
  We examine neonatal mortality (death within the first 28 days after birth) as the main outcome measure.
  
  
  RESULTS
  The pooled SGA prevalence was 23.7% (95% CI, 16.5%-31.0%) using the INTERGROWTH-21st standard compared with 36.0% (95% CI, 27.0%-45.0%) with the US 2000 reference. The relative decrease in prevalence was larger among infants born at 33 to less than 37 weeks' gestation compared with term infants. The pooled neonatal mortality risk did not differ significantly; the adjusted risk ratios were 2.13 (95% CI, 1.78-2.54; P < .001) for the INTERGROWTH-21st standard and 2.12 (95% CI, 1.81-2.48; P < .001) for the US 2000 reference.
  
  
  CONCLUSIONS
  To our knowledge, INTERGROWTH-21st is the first international newborn standard for size for gestational age for healthy fetal growth. We observed a greater-than-one-quarter reduction in SGA prevalence and no significant change in the associated neonatal mortality risk, resulting in a decrease in the percentage of neonatal death attributable to SGA. Our study sheds light on how previously published studies on SGA status may be reinterpreted with the introduction of this new birth weight standard.
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Naoko
authors.initials: N
authors.lastname: Kozuki
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Joanne
authors.initials: J
authors.lastname: Katz
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Parul
authors.initials: P
authors.lastname: Christian
authors.affiliation: Department of Pediatric Newborn Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Anne C C
authors.initials: AC
authors.lastname: Lee
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland3Department of Population, Family, and Reproductive Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.affiliation: Programa de Pós-graduacao em Epidemiologia, Universidade Federal de Pelotas, Pelotas, Rio Grande do Sul, Brazil.
authors.forename: Mariangela F
authors.initials: MF
authors.lastname: Silveira
authors.affiliation: Programa de Pós-graduacao em Epidemiologia, Universidade Federal de Pelotas, Pelotas, Rio Grande do Sul, Brazil.
authors.forename: Fernando
authors.initials: F
authors.lastname: Barros
authors.affiliation: Department of Global Health, George Washington University Milken Institute School of Public Health, Washington, DC.
authors.forename: James M
authors.initials: JM
authors.lastname: Tielsch
authors.affiliation: Centre for Medical Parasitology, Department of Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Christentze
authors.initials: C
authors.lastname: Schmiegelow
authors.affiliation: Department of Global Health and Population, Harvard School of Public Health, Boston, Massachusetts.
authors.forename: Ayesha
authors.initials: A
authors.lastname: Sania
authors.affiliation: Nutrition and Child Health Unit, Institute of Tropical Medicine, Antwerpen, Belgium.
authors.forename: Dominique
authors.initials: D
authors.lastname: Roberfroid
authors.affiliation: Vector Control Division, Ministry of Health, Kampala, Uganda.
authors.forename: Richard
authors.initials: R
authors.lastname: Ndyomugyenyi
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Luke C
authors.initials: LC
authors.lastname: Mullany
authors.affiliation: ASEAN Institute for Health Development, Mahidol University, Nakhon Pathom, Thailand.
authors.forename: Aroonsri
authors.initials: A
authors.lastname: Mongkolchati
authors.affiliation: Department of Food Safety and Food Quality, Ghent University, Ghent, Belgium12Poverty, Nutrition and Health Division, International Food Policy Research Institute, Washington, DC.
authors.forename: Lieven
authors.initials: L
authors.lastname: Huybregts
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland13ZVITAMBO, Borrowdale, Harare, Zimbabwe.
authors.forename: Jean
authors.initials: J
authors.lastname: Humphrey
authors.affiliation: Department of Global Health and Population, Harvard School of Public Health, Boston, Massachusetts14Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts15Department of Epidemiology, Harvard School of Public Health, Boston, Massa.
authors.forename: Wafaie
authors.initials: W
authors.lastname: Fawzi
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Abdullah H
authors.initials: AH
authors.lastname: Baqui
authors.affiliation: University of North Carolina School of Public Health, Chapel Hill.
authors.forename: Linda
authors.initials: L
authors.lastname: Adair
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Vanessa M
authors.initials: VM
authors.lastname: Oddo
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Black
mesh_terms: D001724:Birth Weight; D005260:Female; D047109:Fetal Development; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D008297:Male; D015995:Prevalence; D011446:Prospective Studies; D012016:Reference Values; D014481:United States