Ambulatory blood pressure monitoring in pregnancy: what is normal?

Noninvasive 24-hour ambulatory blood pressure monitoring holds great promise as a useful tool in the management of hypertensive pregnancies and pregnancies considered "at risk" for development of preeclampsia. The purpose of this study was to define ambulatory blood pressure monitoring parameters throughout normal pregnancy, including women considered at risk for development of hypertension who continued to have a completely normal pregnancy.

Two hundred seventy-six 24-hour ambulatory blood pressure monitoring studies were made cross-sectionally with use of a Spacelabs 90207 device (validated for use in pregnancy), at one or more of 9 to 17, 18 to 22, 26 to 30, and >30 weeks' gestation. Upper limits of normal were defined as the mean plus 2 SDs for awake and sleep ambulatory blood pressure monitoring results at each stage.

Average awake upper limits of normal were 130/77, 132/79, 133/81, and 135/86 mm Hg at the four stages of pregnancy, respectively. Systolic blood pressure fell significantly by 12% to 14% (p < 0.0001) and diastolic blood pressure by 18% to 19% (p < 0.0001) during sleep at all stages of pregnancy. Awake ambulatory blood pressure monitoring systolic measurements were 11 to 12 mm Hg higher than "clinic" measurements (p < 0.001) and diastolic measurements were 5 to 11 mm Hg higher (p < 0.0001) throughout pregnancy. Maximum blood pressure variability ranged from 8 to 13 mm Hg.

The upper limits of normal ambulatory blood pressure monitoring-derived measurements rise slightly as pregnancy progresses. Awake measurements are higher than "clinic" measurements recorded under relaxed conditions by a clinical researcher. The diurnal blood pressure fall and variabilities are similar during pregnancy to those seen in nonpregnant subjects. These data should provide valuable references for further studies of ambulatory blood pressure monitoring in high risk pregnancies.