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Paediatr Perinat Epidemiol. 2016 Sep;30(5):450-61. doi: 10.1111/ppe.12298. Epub 2016 May 16.

Country-Specific vs. Common Birthweight-for-Gestational Age References to Identify Small for Gestational Age Infants Born at 24-28 weeks: An International Study.

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Maternal-Infant Care Research Centre, Mount Sinai Hospital, Canadian Neonatal Network, Toronto, ON, Canada.
Swedish Neonatal Quality Register, Department of Women's and Children's Health, Uppsala University, Uppsala, Sweden.
Gertner Institute for Epidemiology and Health Policy Research, Sheba Medical Centre, Israel Neonatal Network, Tel Hashomer, Israel.
Australia and New Zealand Neonatal Network, Department of Paediatrics, University of Otago, Christchurch, New Zealand.
Department of Social Medicine, National Center for Child Health and Development, Neonatal Research Network Japan, Setagaya-ku, Tokyo, Japan.
Neonatal Data Analysis Unit, Section of Neonatal Medicine, Department of Medicine, Imperial College London, UK Neonatal Collaborative, London, UK.
Swiss Neonatal Network, Department of Neonatology, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
Neonatal Research Network Japan, Maternal and Perinatal Center, Tokyo Women's Medical University, Shinjuku, Tokyo, Japan.
Australian and New Zealand Neonatal Network, Royal Hospital for Women, National Perinatal Epidemiology and Statistic Unit, University of New South Wales, Randwick, NSW, Australia.
Spanish Neonatal Network, Hospital Universitario de Salamanca, Valencia, Spain.
Swedish Neonatal Quality Register, Department of Pediatrics/Neonatal Services, Umeå University Hospital, Umeå, Sweden.
Neonatal Research Network Japan, Department of Health Policy, National Center for Child Health and Development, Setagaya-ku, Tokyo, Japan.
Spanish Neonatal Network, Health Research Institute La Fe, Valencia, Spain.



Controversy exists as to whether birthweight-for-gestational age references used to classify infants as small for gestational age (SGA) should be country specific or based on an international (common) standard. We examined whether different birthweight-for-gestational age references affected the association of SGA with adverse outcomes among very preterm neonates.


Singleton infants (n = 23 788) of 24(0) -28(6) weeks' gestational age in nine high-resource countries were classified as SGA (<10th centile) using common and country-specific references based on birthweight and estimated fetal weight (EFW). For each reference, the adjusted relative risk (aRR) for the association of SGA with composite outcome of mortality or major morbidity was estimated.


The percentage of infants classified as SGA differed slightly for common compared with country specific for birthweight references [9.9% (95% CI 9.5, 10.2) vs. 11.1% (95% CI 10.7, 11.5)] and for EFW references [28.6% (95% CI 28.0, 29.2) vs. 24.6% (95% CI 24.1, 25.2)]. The association of SGA with the composite outcome was similar when using common or country-specific references for the total sample for birthweight [aRRs 1.47 (95% CI 1.43, 1.51) and 1.48 (95% CI 1.44, 1.53) respectively] and for EFW references [aRRs 1.35 (95% CI 1.31, 1.38) and 1.39 (95% CI 1.35, 1.43) respectively].


Small for gestational age is associated with higher mortality and morbidity in infants born <29 weeks' gestational age. Although common and country-specific birthweight/EFW references identified slightly different proportions of SGA infants, the risk of the composite outcome was comparable.


Infant, Extremely Premature; Infant, Small for Gestational Age; Neonatal outcomes

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