Blood pressure measured telemetrically from home throughout pregnancy

Sixty-eight healthy pregnant women measured their blood pressure at home for 1 day every 4 weeks from 14 weeks' gestation until delivery. Blood pressure measurements were made with the Cambridge blood pressure telemetry system, which was composed of a Dinamap 1846 monitor linked to and controlled by a dedicated microprocessor which communicated transtelephonically with a hospital-based microcomputer. On each measurement day each woman measured her blood pressure five times: on first rising and then at 10 AM, 2 PM, 6 PM and 10 PM. At each measurement session the blood pressure was automatically taken 10 times at 1-minute intervals. A total of 23,790 individual blood pressure measurements were analyzed. Systolic, diastolic, and mean arterial blood pressures were lowest at 18 weeks' gestation, rising slowly thereafter at a rate of 0.4 mm Hg systolic and 0.2 mm Hg diastolic per week. The maternal pulse rate also increased steadily after 18 weeks at a rate of 0.25 beats/min per week. There was a strong correlation between the blood pressures at 18, 26, and 38 weeks. All blood pressure parameters were significantly lower on first rising than at other times of the day, although the differences were small: 5 mm Hg for systolic, 4 mm Hg for mean arterial, and 3 mm Hg for diastolic blood pressure. After 10 AM, however, there was no significant daytime variation in any blood pressure parameter, indicating that for most purposes the time of day at which pressure measurements are made is unimportant.