Hypertensive Disorders of Pregnancy

Abstract

In normal pregnancy, blood pressure falls to a nadir in the second trimester (average systolic and diastolic blood pressure 5 and 15 mmHg lower than prepregnancy values, respectively), rising to prepregnancy levels in the third trimester. Blood pressure should be measured in the sitting or lateral position with the sphygmomanometer at the level of the heart using a cuff wide enough to cover 80% of the arm circumference. Hypertension is arbitrarily defined as diastolic blood pressure of 90 mmHg or more (muffling of Korotkoff sounds, Point IV) throughout pregnancy. This corresponds to 3 standard deviations above the mean in the first two trimesters and 2 standard deviations above the mean in the third; above this level there is a significant increase in perinatal mortality. The true incidence of hypertension is difficult to establish: overall one third of all maternities are complicated by hypertension, approximately half of these occurring for the first time in labour.