K5 Rather Than K4 for Diastolic Blood Pressure Measurement in Pregnancy

Abstract

There is a wide variation in measurement techniques for recording blood pressure in pregnancy (1). Until 1998, the recommendation of the International Society for the Study of Hypertension in Pregnancy (ISSHP) was that K4, the muffling of sounds, should be taken as the cutoff point for diastolic blood pressure (DBP) in pregnancy. This recommendation was probably based on the premise that due to the hyperdynamic circulation of pregnancy, Korotkoff 5 (K5), the disappearance of sounds, may be audible at cuff pressures down to zero even though K5 had been shown to be closer to intra-arterial DBP than K4 [i.e., K4 overestimates DBP by 11 mm Hg, whereas K5 overestimates DBP by 7 mm Hg (2)]. This was also the basis for the British Hypertension Society's recommendation concerning the use of K4 rather than K5 (3,4). In women with severe hypertension in pregnancy, K5 overestimates DBP by a similar amount (6 mmHg) (5).