Which Korotkoff sound should be used for the diastolic blood pressure in pregnancy?

There is a gathering momentum favouring the adoption of the 5th Korotkoff sound to identify diastolic blood pressure in pregnancy. Our objective was to measure interobserver reliability for indirect blood pressure measurement in pregnancy for systolic and diastolic measurements and to calculate the difference in diastolic pressure measured by the 4th and 5th Korotkoff sounds. To minimize bias we used trained but previously inexperienced observers with proven, normal auditory acuity. The observers were paired in 4 teams and performed a series of 334 blinded, simultaneous observations of systolic and diastolic blood pressure measurements taken from pregnant women between 12-41 weeks' gestation. Reliability was measured by intraclass correlation coefficient for paired measures and kappa for the detection or nondetection of 4th (K4) and 5th (K5) Korotkoff sounds. K4 was undetected in 36% of observations and K5 was undetected in 2% of observations. Reliability for detection or nondetection of Korotkoff sounds was fair for K4 (kappa 0.36) and moderate for K5 (kappa 0.58). Reliability was good between observers for systolic, K4 and K5 diastolic measurements (intraclass correlation > or = 0.80). The mean difference between the diastolic pressure measured by K4 and K5 was 15 mmHg for all measurements and 8 mmHg for the top quartile of measurements (p <0.001). We found K5 to be more often and more reliably detected than K4. If units adopt K5 in preference to K4, consideration will need to be given to lowering treatment thresholds for women with borderline or mild hypertension.