Previous research has supported the importance of temperature in favoring the evolution of viviparity. However, recent research with squamate reptiles (the group with the most extant evolutionary origins of viviparity among terrestrial amniotes), suggests that low oxygen availability at high elevations could also be an important factor underlying the origins of viviparity. If hypoxia favors the evolution of viviparity, then 1) hypoxia should lead to a decrease in offspring fitness, 2) gravid females should be able to provide a similar or enhanced oxygen environment compared to an egg at high elevations, and 3) females should be able to behaviorally and physiologically accommodate to increase oxygen availability to the developing embryo. By canvassing the existing literature, we found that eggs incubated in hypoxic environments result in embryos with reduced viability and increased frequency of developmental anomalies. Hatchlings that developed in hypoxia are also smaller which can reduce fitness. However, we found that the maternal blood environment may be normoxic relative to the environment available to eggs at high elevations. Mechanisms supporting this include increased respiration rate and hemoglobin concentration that increase oxygen availability to embryos. Viviparous females also have maternal and extraembryonic tissues that can promote enhanced vascular gas exchange between the embryonic and maternal tissues. Together, these results highlight potential physiological mechanisms whereby hypoxia could influence the evolution of viviparity.