Differences between office and 24-hour ambulatory blood pressure measurement during pregnancy.

OBJECTIVE: To compare blood pressure (BP) measurements in ambulatory pregnant women with well-taken office readings. METHODS: A cohort of 209 nulliparous pregnant women who underwent 24-hour ambulatory BP monitoring throughout pregnancy was studied; 62 of these women were also studied 12 weeks after delivery. In addition, 30 nulligravid, nonpregnant women were studied as controls. RESULTS: The 24-hour median systolic and diastolic ambulatory pressures were higher than office pressures during pregnancy (the differences between the office and ambulatory systolic and diastolic BP measurements were +5 and +5.5 mmHg at 18 weeks, +3 and +6.5 mmHg at 28 weeks, and +5 and +5.5 mmHg at 36 weeks, P < .001). Ambulatory BP showed a consistent rise over the three measurement points, resulting in higher levels of pressure at 36 weeks than those found 12 weeks after delivery (the difference between ambulatory BP at these measurement points was +5 and +1 mmHg). At the postpartum measurement point, the relationship between ambulatory and office BP was similar to that in other surveys in nonpregnant women of comparable ages and in our own control group of nulligravidas (the difference between ambulatory and office BPs after delivery was +1.5 and +2 mmHg, a nonsignificant difference). CONCLUSION: There are important differences between ambulatory and office BPs measured throughout pregnancy, findings that could not be explained by activity or our present knowledge of cardiovascular hemodynamics in pregnancy. Ambulatory BP readings must be considered different entities than office BP readings. Care should be taken in predicting obstetric outcome from the results of ambulatory BP recordings.