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Measurement of of blood pressure in pregnancy

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Blood pressure is a clinical measurement and as such should be measured as accurately as possible on all occasions. Early work carried out on blood pressure measurement in pregnancy demonstrated that the muffling of sounds (Korotkov phase IV), when taking blood pressure using the standard technique, with a mercury manometer, more accurately represented the level of diastolic blood pressure. Normally in the non-pregnant individual the diastolic blood pressure is "read off" the manometer on the disappearance of sounds, Korotkov phase V. There are many reasons why this is a better measure in the non-pregnant individual. However the early work referred to above claimed that in pregnancy the muffling of sounds was frequently heard down to zero on the mercury column(Reference1,Reference2). In patients where K5 occurred the researchers claimed that the gap between phase IV and phase V was so great as to render phase V inaccurate. For many years, based upon this work, Korotkov phase IV, the muffling of sounds, was recommended by all bodies, such as the WHO, ISSHP and ASSHP for the measurement of diastolic blood pressure in pregnancy.

Subsequent research has revealed that these assertions are wrong and that Korotkov phase V, the disappearance of sounds, should be used as the measure of diastolic blood pressure in pregnancy (Reference3). It was demonstrated that the muffling of sounds were very rarely audible to the zero level (Reference4) on the mercury column. The research also showed that the difference between phase IV and phase V was about 2 - 3 mmHg in pregnancy which is clinically insignificant. Other work using intra-arterial measurements of blood pressure also confirmed that Korotkov's phase V was the most accurate measure of diastolic blood pressure in pregnancy (Reference5,Reference6).


Recommendations for taking blood pressure:

  • Blood pressure measurements need to be both accurate and reproducible between observers. Measurement devices such as sphygmomanometers or automated devices should be well maintained and regularly calibrated.
  • The correct size upper arm cuff should be used. The bladder of the cuff should encompass 80% of the upper arm, if the cuff size is too small it could result in an over estimation of blood pressure by up to 10 mmHg. A blood pressure cuff which is too large could lead to a similar under estimation.
  • Be aware of the white coat effect. This can be minimised by ensuring that the patient is relaxed and comfortable before the blood pressure measurements are taken.
  • When measuring blood pressure in an individual 2 readings should be taken. The second reading is nearly always lower that the first and is a truer representation of blood pressure. The British Hypertension Society produced guidelines on the technique of blood pressure measurement and should be referred to as the gold standard of for blood pressure for measurement technique.



1. Davey DA. The classification and definition of the hypertensive disorders of pregnancy. Am J Obstet Gynecol 1988;58:892-8, Abstract
2. Wichman K. The influence of different positions and Korotkoff sounds on the blood pressure measurements in pregnancy. Acta Obstet Gynecol Scand 1984;118(supp1):25-8, Abstract
3. Lopez MC. The measurements of diastolic blood pressure during pregnancy: which Korotkoff phase should be used. Am J Obstet Gynecol 1994;170:574-8, Abstract
4. Walker SP. The diastolic debate: is it time to discard Korotkoff phase IV in favour of phase V for blood pressure measurements in pregnancy? Med J Aust 1998;169:203-5, Abstract
5. Rattery EB. The indirect method of recording blood pressure. Cardiovasc. Res 1968;2:210-8
6. Brown MA. Measuring blood pressure in pregnant women: a comparison of direct and indirect methods. Am J Obstet Gynecol 1994;171:661-7, Abstract

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