Low oxygen, as is common at high altitudes, poses major challenges to the body. These effects are well-described with respect to activities like exercise; however, low oxygen also challenges reproduction. Across mammals, low oxygen found at high altitudes leads to greater risk for pregnancy complications, especially low birth weight. Even though understanding how this happens could help us predict and prevent these poor outcomes, the processes by which low oxygen influences pregnancy and fetal growth trajectories remains poorly understood. This research will test the hypothesis that maternal metabolism and its response to low oxygen are important factors that determine pregnancy outcomes and fetal growth at high altitudes. The research uses a rodent model, the North American deer mouse, for which some populations have resided at high altitude for many generations and no longer experience birth weight reductions at high altitude. The research aims will compare how low oxygen alters the maternal physiology of high-altitude deer mice (that don’t experience birth weight reductions) versus low altitude-resident deer (which do experience birth weight reductions). The proposed experiments will also use advanced genetic and genomic tools to determine how the expression of key genes in the placenta influence maternal metabolism. This work will advance our basic understanding of how reproductive biology contributes to mammalian adaptation while also providing new perspectives on some o