Presented by Dr. Jimmy Breen, University of Adelaide The human placenta is the largest fetal organ and is important during pregnancy. However, very little is known about its development and function during gestation. Using RNA sequencing, placental chorionic villous tissues from 96 pregnancies at six to 23 weeks of gestation were profiled. Substantial changes in gene expression between early and late gestation were identified, the majority of which were enriched in functions relating to transcription factor signalling, inflammatory response and cell adhesion. Using co-expression network and gene set enrichment analyses, three distinct phases of gene expression coincident with phases of maternal blood flow to the placenta were discovered. They impact immune function and are likely driven by oxygen tension, potentially in a sex-specific manner. Future efforts to improve how pregnancy complications are treated will be discussed.