Temporal placental genome wide expression profiles reflect three phases of utero-placental blood flow during early to mid human gestation

During early human placental development, extravillous cytotrophoblasts (EVT) invade the uterine vasculature to sequester a maternal blood supply. The impact of this on placental gene expression has not been established for normal pregnancy. Using RNA sequencing, we profiled placental chorionic villous tissues from 96 pregnancies at 6-23 weeks of gestation. We identified 1,048 genes that were differentially expressed between 6-10 weeks’ and 11-23 weeks’ of gestation. These are predominantly genes that are enriched in transcription factor signalling, inflammatory response and cell adhesion. Using a co-expression network and gene set enrichment analyses, we reveal three distinct phases of gene expression coincident with phases of maternal blood flow to the placenta that impact immune function and are likely driven by oxygen tension, potentially in a sex-specific manner. These data represent a comprehensive transcriptional profile of early placental development and point to significant environmental, genetic and regulatory triggers that drive gene expression.