Abstract The maternal fetal interface is hormonal and immunologically rich environment that is important for normal placentation during the first trimester of pregnancy. This is also where adult diseases have developmental origins. Both the hormonal and immunologic milieus at this stage of gestation are already sexually dimorphic. We identified sexually dimorphic gene expression globally and among individual cell types of the first trimester placenta impacted by signaling at the maternal fetal interface, which includes members of the TGF-β superfamily, specifically TGFβ-1 and BMPs in males. Among individual cell types, ligands from the CCL family were most highly representative in females whereas IL1RN and MMP9 were highly expressed in males, with their corresponding receptors present on the maternal surface. Dihydrotestosterone, which is only produced by the male fetus, in addition to TGFβ1 and estradiol were identified as significant upstream regulators in individual cell types of the first trimester placenta. However, the hormonal environment may not be the only biologically sex different factor influencing the immune system, as we have also identified key transcription regulators in early gestation that may account for developmental origins of immune disease. Throughout the lifespan, hormones have been implicated to play a significant role in immune dysfunction and development of disease, as overall there is a higher prevalence of autoimmune diseases in females, such as systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis. Yet men are more likely to develop ankylosing spondylitis. Furthermore, males have increased prevalence of asthma compared to females in childhood, but the prevalence changes post-puberty, suggesting testosterone may be protective. Therefore, in order to better understand the influence of sex during developmental origins of immune function, including the effect of the hormonal milieu, we intend to identify sex specific transcriptional regulatory signatures in the first trimester placenta. Furthermore, since sex hormones are not dimorphic in early childhood, prior to puberty, we intend to better understand differences during development of the immune system at birth. Our goal is to identify sex unique regulators of immune dysfunction that can ultimately be used as a more personalized approach to treating immunologic diseases.