Problem: There is growing evidence for the role of placental inflammation in the pathophysiology of pregnancy complications including fetal growth restriction (FGR). This study aimed to characterize the inflammatory profile in the maternal circulation and the placenta of infants who were growth restricted and those that were small for gestational age (SGA). Method of study: Placental villous tissue and maternal serum were obtained from pregnancies where infants were SGA at birth or who had a decreasing growth rate (≥25 centiles) across the third trimester. Immunohistochemical and histological analyses of placental samples were conducted for macrophage number, alongside vascular and cell turnover analysis. Inflammatory profile was analyzed in maternal and placental compartments via ELISAs and multiplex assays. Results: There were significantly more CD163
+ macrophages in placentas of infants with a decreased growth rate compared to controls, but not in SGA infants (median 8.6/ nuclei vs 3.8 and 2.9, P =.008 and P =.003, respectively). Uric acid (P =.0007) and IL-8 (P =.0008) were increased in placentas, and S100A8 (P <.0002) was increased in maternal serum of infants with decreased growth rate. No changes in the maternal serum or placental lysates of SGA infants were observed. Conclusion: The evidence of an altered inflammatory profile in infants with a decreasing growth rate, but not in those that were born SGA, provides further evidence that inflammation plays a role in true FGR. It remains unclear whether the increased placental macrophages occur as a direct result, or as a consequence of the pro-inflammatory environment observed in fetal growth restriction.