To determine the effects of tobacco smoke on the placental transcriptome, Bruchova et al. performed gene expression profiling in term placentas from women exposed to tobacco smoke in pregnancy and from those without significant exposure. Smoking status of the women was defined based on questionnaire data supported by cotinine plasma concentrations. Villus parenchymal sections were obtained by dissecting a 1.5 cm² segment approximately 5 cm from the cord insertion site and then splitting it into three equal parts: maternal (including the thin basal plate), middle, and fetal (including the chorionic plate). Total RNA was isolated from the middle section.