The pregnant woman is at risk of several pregnancy-specific conditions that may cause respiratory failure, as well as many conditions that are aggravated by the pregnant state. These conditions include pulmonary edema secondary to preeclampsia, amniotic fluid embolism, ARDS due to pregnancy complications and other causes, as well as aspiration of gastric contents, venous thromboembolism and pre-existing heart disease. Management of these patients requires understanding of the altered maternal physiology and avoidance of harm to the fetus. While radiological procedures and drug therapy may compromise fetal wellbeing, the greatest risk is deterioration in the maternal condition resulting in fetal hypoxia. Little data exist to guide prolonged mechanical ventilation in the pregnant woman, but usual principles can be applied to optimize oxygenation, while avoiding maternal alkalosis. If the fetus is at a viable gestation and is at risk due to intractable maternal hypoxia, there may be a benefit to the fetus in delivery. However, delivery purely in an attempt to improve maternal oxygenation or ventilation is often not successful.