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Background: Infants born small for gestational age (SGA) as well as those born prematurely are at increased risk for postnatal growth failure (PGF), mostly due to more severe postnatal weight loss and early neonatal morbidities. Generally, intrauterine growth restriction (IUGR) increases morbidity and mortality among very preterm neonates. PGF is classically referred to as a condition in which extrauterine growth is less than expected based on intrauterine growth measurements. A large number of studies have documented a strong correlation between size at birth and subsequent weight, although the reported incidence of catch-up growth and consequently the impact on final weight has varied with time and between countries. These variations may be real, but could also be related to a number of methodological problems and the evidence supporting this association is scarce and has not been systematically reviewed. The aim of this study was to assess the risk of PGF associated with SGA birth among low birth weight infants. We paid specific consideration to how the criteria used to define neonatal growth restriction at birth and PGF affected the potential association between the two conditions.

Methods: A three-step search strategy was employed. PubMed/MEDLINE, the Cochrane library, the JBI Library, SciELO databases were searched. The search for unpublished studies were Google, Google Scholar and conference proceedings. PGF status of LBW infants, quantified by using weight/length/head circumference and gestational age measurements were extracted and compared between SGA/IUGR group and appropriate for gestational age (AGA) group by way of a random effects model. Sources of heterogeneity were determined by subgroup and meta-regression analyses. The protocol has be registered: registration number is CRD42019141172.

Results: Ten independent studies with 35906 LBW infants were included in this systematic review and meta-analysis. The analysis revealed a significantly increased risk of PGF in the SGA group when compared to AGA group with a relative risk (RR) of 1.71, and a 95% confidence interval (CI) of 1.1 to 2.64. Moreover, a stronger statistically significantly increased risk of PGF was observed in studies defining neonatal growth restriction as BW <3^rd percentile (RR = 2.13)

Conclusion: The present systematic review and meta-analysis could provide conclusive evidence on the association between SGA and PGF risk. Relative to AGA, SGA/IUGR birth was associated with an increased risks of PGF. The rate of PGF was significantly increased among extremely preterm births of SGA groups compared to extremely preterm births of AGA groups. Low quality of evidence as examined which shows further investigation is needed to change the estimate.