Randomised trial of management of hypertensive pregnancies by Korotkoff phase IV or phase V

Background There is debate about whether diastolic blood pressure should be recorded as the fourth (muffling, K4) or fifth (disappearance, K5) Korotkoff sound in pregnancy. We compared maternal and fetal outcomes and the likelihood that episodes of severe hypertension would be recorded when hypertensive pregnancies were managed according to either K4 or K5.

Methods 220 pregnant women with diastolic hypertension (K4 greater than or equal to 90 mm Hg) after the 20th week of gestation were enrolled in a prospective randomised study at two obstetric units in Australia; they were randomly assigned management with K4 (n=103) or K5 (n=117) for the remainder of the pregnancy. Clinical management was according to a uniform department protocol. Analysis was by intention to treat. All the women completed the trial.

Findings An episode of severe hypertension (systolic greater than or equal to 170 mm Hg, diastolic greater than or equal to 110 mm Hg, or both) was more likely to be recorded with use of K4 than with use of K5 (39 [38%] vs 30 [26%] women, p=0.051), mainly because of a greater likelihood that severe diastolic hypertension would be recorded (34 [33%] vs 20 [17%], p=0.006). The frequency of severe systolic hypertension and simultaneous severe systolic and diastolic hypertension did not differ between groups. Pregnancy was prolonged by an average of 2 weeks in both groups, and there were no significant differences between the groups in laboratory data, requirements for antihypertensive treatment, birthweight, fetal growth retardation, or perinatal mortality. There was no eclampsia or significant maternal morbidity in either group.

Interpretation A change from use of K4 to K5 would mean that one fewer case of severe diastolic hypertension would be recorded for every six hypertensive pregnancies, but all other episodes of severe hypertension would be recorded with similar frequency. Since the K4/K5 difference is smaller in hypertensive than in normotensive pregnant women and since K5 is closer to the actual intra-arterial pressure and more reliably detected, universal adoption of K5 to record diastolic blood pressure in hypertensive pregnancy should be considered.