Gestational diabetes mellitus is associated with increased CD163 expression and iron storage in the placenta

GDM has been associated with disturbances in iron homeostasis and exaggerated immune activation. We sought to investigate the extent to which placental iron storage and macrophage accumulations were altered in GDM.

We conducted a retrospective, case-control study of archived placental tissues obtained from 22 pregnancies complicated by GDM and 22 unaffected controls. Controls were matched to cases based on maternal age, gestational age at birth, and method of delivery. Placental tissues were assessed for altered histology and CD68 and CD163 staining. Tissue iron was assessed using Prussian blue staining.

Maternal hematocrit levels were higher in GDM participants compared to controls (P = 0.02). The presence of meconium-laden macrophages was significantly greater within the amnion of GDM cases (adjusted odds ratio (OR) 12.51). Although the total abundance of CD68-expressing macrophages was not significantly different between groups, we detected a significantly greater abundance of CD163 expression within the chorion and decidua of cases. The total area staining positive for iron was 24% (95% confidence intervals of 2%-46%) greater in GDM placentae versus controls.

GDM is associated with altered placental histology and increases in meconium-laden macrophages. Greater iron stores within the placentae of women with GDM is consistent with reports that iron excess is associated with an increased risk for GDM. The higher level of expression of CD163 on macrophage-like cells of the chorion and decidua in GDM suggests an increase in M2-like macrophages. Overall, our results add to growing evidence that GDM has direct effects on placental structure.