Approximately 1% of maternity patients require ICU admission, the most common causes being obstetric haemorrhage and pre-eclampsia. This chapter discusses the physiological changes occurring in the cardiovascular system and respiratory system during pregnancy, and the obstetric emergencies. The obsetetric emergencies include pulmonary embolism, venous thromboembolism (VTE), amniotic fluid embolism (AFE), obstetric haemorrhage, ovarian hyperstimulation syndrome (OHSS), and sepsis. VTE may occur at any time during pregnancy but is most common during the puerperium. AFE is a spectrum of disease that may range from subclinical to cardio-respiratory collapse and death. OHSS can occur in up to 10% of patients undergoing in vitro fertilization (IVF) but the vast majority will have no or mild problems. The onset of life-threatening sepsis in the pregnant woman can be insidious, with rapid deterioration, and fever may not always be present.