Pregnancy is a hypercoagulable state, making pulmonary embolism a special consideration.
In this regard, her country of origin is notable, because it suggests a risk of Chagas' disease, rheumatic heart disease, or both. Rheumatic heart disease is associated with a childhood history of fever and arthralgias. She should be asked specifically about childhood illnesses.
Adequate fetal oxygenation requires a maternal partial pressure of arterial oxygen (PaO2) of 70 mm Hg or higher, corresponding to an arterial oxygen saturation of approximately 95%.
Fetal PaCO2 clearance by the placenta requires a gradient of approximately 10 mm Hg; to achieve this goal, the maternal PaCO2 should remain less than 45 mm Hg and the pH should be greater than 7.3.
Its prevalence is high in sub-Saharan Africa, south central Asia, and the Pacific Islands and in indigenous populations of Australia and New Zealand (range, 2.2 to 5.7 cases per 1000 persons).