• Joanne Katz, Anne Cc Lee, Naoko Kozuki, Joy E Lawn, Simon Cousens, Hannah Blencowe, Majid Ezzati, Zulfiqar A Bhutta, Tanya Marchant, Barbara A Willey, Linda Adair, Fernando Barros, Abdullah H Baqui, Parul Christian, Wafaie Fawzi, Rogelio Gonzalez, Jean Humphrey, Lieven Huybregts, Patrick Kolsteren, Aroonsri Mongkolchati, Luke C Mullany, Richard Ndyomugyenyi, Jyh Kae Nien, David Osrin, Dominique Roberfroid, Ayesha Sania, Christentze Schmiegelow, Mariangela F Silveira, James Tielsch, Anjana Vaidya, Sithembiso C Velaphi, Cesar G Victora, Deborah Watson-Jones, Robert E Black, and CHERG Small-for-Gestational-Age-Preterm Birth Working Group.
• Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD USA. Electronic address: jkatz@jhsph.edu.
• Lancet. 2013 Aug 3; 382 (9890): 417425417-425.

BackgroundBabies 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.MethodsFor 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.FindingsPooled 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).InterpretationMany 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.FundingBill & Melinda Gates Foundation.Copyright © 2013 Elsevier Ltd. All rights reserved.

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