Managing critically ill obstetric patients in the ICU is a challenge because of their altered physiology, different normal ranges for laboratory and clinical parameters in pregnancy, and potentially harmful effects of drugs and interventions on the fetus. About 200 to 700 women per 100,000 deliveries require ICU admission. A systematic five-step approach is recommended to enhance maternal and fetal outcomes: (1) differentiate between medical and obstetric disorders with similar manifestations, (2) identify and treat organ dysfunction, (3) assess maternal and fetal risk from continuing pregnancy and decide if delivery/termination of pregnancy will improve outcome, (4) choose an appropriate mode of delivery if necessary, and (5) optimize organ functions for safe delivery. A multidisciplinary team including the intensivist, obstetrician, maternal-fetal medicine specialist, anesthesiologist, neonatologist, nursing specialist, and transfusion medicine expert is key to optimize outcomes. Severe preeclampsia and its complications, HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome, and amniotic fluid embolism, which cause significant organ failure, are reviewed. Obstetric conditions that were not so common in the past are increasingly seen in the ICU. Thrombotic thrombocytopenic purpura of pregnancy is being diagnosed more frequently. Massive hemorrhage from adherent placenta is increasing because of the large number of pregnant women with scars from previous cesarean section. With more complex fetal surgical interventions being performed for congenital disorders, maternal complications are increasing. Ovarian hyperstimulation syndrome is also becoming common because of treatment of infertility with assisted reproduction techniques. Part II will deal with common medical disorders and their management in critically ill pregnant women.