title: Mortality risk in preterm and small-for-gestational-age infants in low-income and middle-income countries: a pooled country analysis.
abstract: BACKGROUND
  Babies with low birthweight (<2500 g) are at increased risk of early mortality. However, low birthweight includes babies born preterm and with fetal growth restriction, and not all these infants have a birthweight less than 2500 g. We estimated the neonatal and infant mortality associated with these two characteristics in low-income and middle-income countries.
  
  
  METHODS
  For this pooled analysis, we searched all available studies and identified 20 cohorts (providing data for 2,015,019 livebirths) from Asia, Africa, and Latin America that recorded data for birthweight, gestational age, and vital statistics through 28 days of life. Study dates ranged from 1982 through to 2010. We calculated relative risks (RR) and risk differences (RD) for mortality associated with preterm birth (<32 weeks, 32 weeks to <34 weeks, 34 weeks to <37 weeks), small-for-gestational-age (SGA; babies with birthweight in the lowest third percentile and between the third and tenth percentile of a US reference population), and preterm and SGA combinations.
  
  
  RESULTS
  Pooled overall RRs for preterm were 6·82 (95% CI 3·56-13·07) for neonatal mortality and 2·50 (1·48-4·22) for post-neonatal mortality. Pooled RRs for babies who were SGA (with birthweight in the lowest tenth percentile of the reference population) were 1·83 (95% CI 1·34-2·50) for neonatal mortality and 1·90 (1·32-2·73) for post-neonatal mortality. The neonatal mortality risk of babies who were both preterm and SGA was higher than that of babies with either characteristic alone (15·42; 9·11-26·12).
  
  
  CONCLUSIONS
  Many babies in low-income and middle-income countries are SGA. Preterm birth affects a smaller number of neonates than does SGA, but is associated with a higher mortality risk. The mortality risks associated with both characteristics extend beyond the neonatal period. Differentiation of the burden and risk of babies born preterm and SGA rather than with low birthweight could guide prevention and management strategies to speed progress towards Millennium Development Goal 4--the reduction of child mortality.
  
  
  BACKGROUND
  Bill & Melinda Gates Foundation.
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA. Electronic address: jkatz@jhsph.edu.
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authors.lastname: Katz
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA; Brigham and Women's Hospital, Boston, MA, USA.
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authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA.
authors.forename: Naoko
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authors.affiliation: Saving Newborn Lives and Save the Children USA, Washington, DC, USA; Maternal Reproductive and Child Health Centre, London School of Hygiene and Tropical Medicine, London, UK.
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authors.affiliation: Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK.
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authors.affiliation: Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK.
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authors.affiliation: MRC-HPA Centre for Environment and Health, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, London, UK.
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authors.affiliation: Division of Women and Child Health, Aga Khan University, Karachi, Pakistan.
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authors.affiliation: Maternal Reproductive and Child Health Centre, London School of Hygiene and Tropical Medicine, London, UK; Faculty of Infectious Disease and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK; Malaria Centre, London School of Hygiene and Tropical Medicine, London, UK.
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authors.lastname: Marchant
authors.affiliation: Maternal Reproductive and Child Health Centre, London School of Hygiene and Tropical Medicine, London, UK; Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK; Malaria Centre, London School of Hygiene and Tropical Medicine, London, UK.
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authors.affiliation: University of North Carolina School of Public Health, NC, USA.
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authors.affiliation: Programa de Pós-graduacao em Epidemiologia, Universidade Federal de Pelotas, Pelotas, RS, Brazil; Programa de Pós-graduação em Saúde e Comportamento, Univertsidade Católica de Pelotas, Centro, Pelotas, RS, Brazil.
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authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA.
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authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA.
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authors.affiliation: Department of Nutrition, Harvard School of Public Health, Boston, MA, USA; Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA; Department of Global Health and Population, Harvard School of Public Health, Boston, MA, USA.
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authors.affiliation: Pontificia Universidad Católica de Chile, School of Medicine, Santiago, Chile; Clínica Santa María, Santiago, Chile.
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authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA; Zvitambo, Borrowdale, Harare, Zimbabwe.
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authors.affiliation: Department of Food Safety and Food Quality, Ghent University, Ghent, Belgium; Woman and Child Health Research Center, Department of Public Health, Institute of Tropical Medicine, Antwerpen, Belgium.
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authors.affiliation: Department of Food Safety and Food Quality, Ghent University, Ghent, Belgium; Woman and Child Health Research Center, Department of Public Health, Institute of Tropical Medicine, Antwerpen, Belgium.
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authors.affiliation: ASEAN Institute for Health Development, Mahidol University, Nakhon Pathom, Thailand.
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authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA.
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authors.affiliation: Fetal Maternal Medicine Unit, Clinica Davila, Santiago, Chile; Faculty of Medicine, Universidad de Los Andes, Santiago, Chile.
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authors.affiliation: Institute for Global Health, UCL Institute of Child Health, London, UK.
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authors.affiliation: Woman and Child Health Research Center, Department of Public Health, Institute of Tropical Medicine, Antwerpen, Belgium.
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authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA.
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authors.affiliation: Centre for Medical Parasitology, Institute of International Health, Immunology, and Microbiology, University of Copenhagen; Department of Infectious Diseases, Copenhagen University Hospital, Copenhagen, Denmark.
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authors.initials: MF
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authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA; Department of Global Health, George Washington School of Public Health and Health Services, George Washington University, Washington, DC, USA.
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authors.affiliation: Institute for Global Health, UCL Institute of Child Health, London, UK.
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authors.affiliation: Department of Paediatrics, Division of Neonatology, Chris Hani Baragwaneth Hospital, University of Witwatersrand, Soweto, South Africa.
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authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA.
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mesh_terms: D017954:Africa South of the Sahara / Q000453:epidemiology; D001208:Asia / Q000453:epidemiology; D006801:Humans; D007182:Income / Q000706:statistics & numerical data*; D007223:Infant; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature; D007236:Infant, Small for Gestational Age; D015995:Prevalence; D012307:Risk Factors; D013020:South America / Q000453:epidemiology