• R S Taylor, G Gamble, L McCowan, and R A North.
• Department of Obstetrics and Gynaecology, University of Auckland, New Zealand.
• Am. J. Hypertens. 2001 Jan 1; 14 (1): 38-43.

AbstractThe aim of this study was to investigate the effect of the definition of daytime and nighttime on ambulatory blood pressure (ABP) in pregnancy. To determine the prevalence of a <10% decrease in mean arterial pressure with sleep (nondipper) in pregnancy and the consistency of nondipper status throughout pregnancy. In a prospective, longitudinal study, 102 pregnant woman underwent 24-h ABP monitoring and recorded sleep patterns at < or = 14, 19 to 22, 27 to 30, 35 to 37 weeks' gestation and 5 to 9 weeks' postpartum. Nighttime was defined by arbitrary hours or actual periods of sleep. Ambulatory blood pressure measurements using the different definitions of nighttime were compared in the total cohort and individual women. Nondipper status of each woman was determined throughout pregnancy and postpartum. At 35 to 37 weeks' gestation, 19% of women napped during the day and 20% were awake during the night. Throughout pregnancy, mean day and night systolic and diastolic ABP measurements were similar whether daytime and nighttime were defined by arbitrary hours or by sleep periods. In individuals, the use of arbitrary hours (day 07:00 to 21:59, night 22:00 to 06:59) compared to sleep periods to define day and night resulted in differences in daytime systolic (SBP) and diastolic blood pressure (DBP) of up to 4 and 5 mm Hg, respectively. Similarly there were individual differences in nighttime SBP up to 10 mm Hg and DBP up to 11 mm Hg. A third of women were nondippers at least once during pregnancy, but only two women were consistent nondippers. The different definitions of day and night did not change group ABP measurements, but resulted in significant variation in ABP measurements in individual pregnant women. Nondippers were common and nondipper status frequently changed during pregnancy.

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