Using RNA-sequencing (RNA-Seq and miRNA-Seq), we analyzed paired villous trophoblast and decidual basalis transcriptomes of 15 women pregnant with singleton gestations grouped as follows: (1) spontaneous preterm birth (PTB) in the setting of amniocentesis-proven intra-amniotic infection (IAI) and histological chorioamnionits (n=5; GA median [range]: 26 [25-31] weeks); (2) spontaneous idiopathic preterm birth (iPTB, n=5, GA: 32 [30-33] weeks); and (3) term normal pregnancy, that delivered a heathy infant by cesarean section in the absence of labor (n=5; GA: 39 [38-39] weeks). The primary goal of this study was to identify differentially expressed transcripts and illuminate molecular mechanisms distinguishing IAI-associated PTBs from spontaneous PTBs in the absence of IAI. We further compared iPTB specimens to term specimens to determine genes differentially regulated with advancing gestational age and following spontaneous PTB without IAI. Finally, we determined transcripts selectively expressed in either the villous trophoblast or decidua basalis in each clinical context. Raw data for this series are not available because consent forms do not allow for public access to raw data.