Measuring blood pressure in pregnant women: a comparison of direct and indirect methods.

OBJECTIVES: Our goals were to determine (1) whether Korotkoff phase IV or V sound was a more accurate measure of diastolic blood pressure in pregnancy and (2) interobserver variability of mercury sphygmomanometry of pregnant women. STUDY
DESIGN: Direct (intraarterial) and indirect (mercury sphygmomanometry) blood pressures were compared in 28 pregnant women. Interobserver variability was assessed in a separate study of 86 pregnant women using four highly trained observers.
RESULTS: (1) Routine sphygmomanometry underestimated direct systolic pressure by 11 (3, 18) mm Hg, p < 0.001 (median, interquartile range of differences). Phase IV Korotkoff sound overestimated direct diastolic pressure by 9 (2, 12) mm Hg (p < 0.001) and phase V by 4 (2, 7) mm Hg (p = 0.04). Phase V-recorded diastolic pressure was closer to direct diastolic pressure significantly more often (75%) than was phase IV-recorded diastolic pressure (21%) (p = 0.003). Mean arterial pressures did not differ significantly according to the method used. (2) Median blood pressures did not differ among the four observers for systolic, diastolic phase IV, or phase V recordings. Maximum difference for blood pressure recording among observers was 4 (2, 6) mm Hg.
CONCLUSIONS: Auscultatory sphygmomanometry in pregnant women underestimates systolic and overestimates diastolic blood pressure, but the phase V Korotkoff sound is more likely to represent the true diastolic pressure than is the phase IV sound.