Background Extrauterine growth restriction (EUGR) among children born very preterm (VPT) is a risk factor for poor neurodevelopment. It is commonly defined as a weight for postmenstrual age (PMA) <10th percentile of postnatal growth references. Fenton’s postnatal references, derived by meta-analysis of national birthweight and child growth charts, are commonly used in clinical care and research. Recently, the Intergrowth (IG) 21st project proposed alternative curves derived from multinational healthy preterm infants based on the hypothesis that normal VPT growth differs from term infants. We used these two approaches to investigate EUGR prevalence in a multinational sample of European VPT infants.

Methods Data come from the EPICE (Effective Perinatal Intensive Care in Europe) project, an area-based study of infants born at less than 32 weeks’ gestation in 2011/12 in 19 regions from 11 European countries. We included 6,471 infants discharged home before 50 weeks PMA. EUGR was defined as weight at discharge for PMA and sex <10th percentile using Fenton and IG references. We compared the prevalence of EUGR by selected neonatal characteristics and country of birth, using X2 tests. We used generalized linear regression models with a Poisson distribution and robust standard errors to estimate adjusted risk ratios (aRR).

Results The prevalence of EUGR using Fenton’s references was 43.9% for boys and 45.2% for girls (NS) compared to 33.6% for boys and 25.5% for girls for IG (p<0.01). Prevalence of EUGR by country ranged from 24.7% in Sweden to 60.1% in Portugal for Fenton and from 14.0% in Sweden to 43.7% in Portugal for IG. Lower gestational age at birth, being small for gestational age at birth and having a severe neonatal morbidity were risk factors for being EUGR, regardless of the reference. Boys were more growth restricted than girls when using IG, but not Fenton. Adjusting for case-mix did not reduce variability between regions: the aRR for EUGR for Portuguese compared to Swedish VPT infants was 2.5 (95% confidence interval (CI): 2.0–3.1) for Fenton and 3.3 (95% CI: 2.6–4.6) for IG.

Conclusion Accurately identifying infants with sub-optimal growth is important for clinical care and for research on the etiology and consequences of EUGR. The difference in EUGR prevalence linked to choice of reference as well as the large variations between countries suggest that references should be validated in their target populations before adoption.