Maternal smoking in early pregnancy disrupts placental function through syncytiotrophoblast and macrophage dysregulation.

Smoking in pregnancy is the leading avoidable cause of gestational morbidity and mortality, causally linked to fetal growth restriction (FGR). The placenta, functional interface between mother and fetus is essential for healthy fetal development. For the first time, we studied cell type-resolved smoking effects on placental development at high molecular resolution using single-nucleus RNA sequencing and deep visual proteomics of matched tissues. We validated our findings through an independent cohort and in-vitro cigarette smoke exposure to primary human trophoblast cells. Our results show placental macrophages (Hofbauer cells; HBC) and the syncytiotrophoblast (STB) barrier are most affected by smoking, with dysregulation of cell-cell adhesion, extracellular matrix organization, and stress phenotype. STBs show moderate compositional increases in smokers and in-silico trophoblast differentiation modelling indicates a preferential shift towards the STB lineage in this group. The trophoblast displays a large upregulation of pro-angiogenic effectors, increases in xenobiotic detoxification, reduced mitochondrial function, and vastly altered transmembrane transport. These molecular changes affect placental development with important consequences for fetal growth. We provide insight into placental dysfunction contributing to FGR early in pregnancy, before clinical symptoms appear. We anticipate this data to advance diagnostics and therapies to improve FGR outcomes.