Significance Children raised in economically disadvantaged households face increased risks of poor health in adulthood, suggesting early origins of socioeconomic inequalities in health. In fact, maternal immune activity in response to stressful conditions during pregnancy has been found to play a key role in fetal brain development. Here we show that socioeconomic disadvantage is associated with lower concentrations of the pro-inflammatory cytokine IL-8 during the third trimester of pregnancy and, in turn, with offspring’s neurologic abnormalities during the first year of life. These results suggest stress–immune mechanisms as one potential pathophysiologic pathway involved in the early origins of population health inequalities.