Maternal oxygen transport variables during the third trimester of normal pregnancy

OBJECTIVE: The aim of this study was to measure and calculate oxygen transport variables in uncomplicated term pregnancies. STUDY DESIGN: Ten normotensive primiparous women between 36 and 38 weeks' gestation underwent pulmonary and radial arterial catheterization as part of a larger study. Seven women had studies repeated at approximately 12 weeks post partum. Measurements were made with patients in the left lateral recumbent position after a 30-minute stabilization period. Cardiac output was measured with the thermodilution technique. Blood samples were obtained simultaneously from the pulmonary and radial arteries and analyzed in duplicate for oxygen content with a blood gas analyzer. RESULTS: The oxygen contents of both arterial and mixed venous blood are significantly lower (P < .05) in the third trimester of pregnancy (15.96 and 11.97 mL/dL, respectively) than in the postpartum period (18.00 and 13.54 mL/dL). The fall in oxygen content during pregnancy prevents any significant increase in oxygen delivery in the third trimester (867.59 mL/min) relative to the postpartum period (806.50 mL/min, P not significant). CONCLUSION: This is the first report of directly measured oxygen transport variables in healthy pregnant women.