Summary: A premeasurement period of 5 minutes quiet resting is recommended prior to measuring blood pressure. The aim of this study was to determine the effect of this period of rest on the level of blood pressure in pregnant women. One hundred pregnant women had their blood pressure measured on a single visit using a QuietTrak ambulatory blood pressure monitor, used to remove human observer bias. Group 1 (n = 50) had blood pressure measured as soon as possible on entering the clinic room and again after 5 minutes rest. Group 2 were rested for 5 minutes on entry to the clinic room prior to the first blood pressure measurement and had the second measurement taken after a further 5 minutes rest. Results were compared in the 2 groups using ANOVA. In Group 1, the initial, mean systolic blood pressure was 116.6 versus 115.5 mmHg taken after 5 minutes quiet rest (p = 0.66). The corresponding diastolic values were 66.2 versus 64.1 (p = 0.40). In Group 2, the initial mean systolic blood pressure was 116.2 versus 115.6 taken after 5 minutes quiet rest (p = 0.85). The corresponding diastolic values were 68.5 versus 65.6 (p = 0.34). Blood pressure was as likely to rise as to fall after a period of quiet rest. It is not necessary to have pregnant women quietly resting during routine visits before having blood pressure measured.