Biopsies were taken from the fetal side of the placenta by cutting into the chorionic plate and sampling of fetal chorionic villi, and preserved in RNALater (Qiagen, USA). To capture variability in gene expression within the placenta, one sampling site was close to the umbilical cord insertion point and one close to the outer margin of the placenta [36 (link)]. We generated gene expression data for 2 biopsies from each of 164 placentas. For some placentas, either tissue was unavailable or the tissue quality and/or quantity were insufficient for analysis, thus, in 12 placentas we relied on 1 biopsy, while we had more than 2 biopsies from 4 placentas. Samples were preserved in RNALater (Qiagen, USA) and stored at -80C. Based on histologic analysis, there was minimal contamination of the biopsies with cells from the chorionic membrane and basal plate [36 (link)].
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