Circadian blood pressure variability in normotensive pregnant women as a function of parity, maternal age, and stage of gestation.

Studies based on conventional office blood pressure (BP) measurements concluded that both maternal age and parity have significant effects on BP during pregnancy. Previous results have also indicated predictable trends of BP variability with gestational age. Accordingly, we have evaluated possible differences in the circadian pattern of ambulatory BP as a function of parity, maternal age, and stage of gestation in normotensive women who were systematically studied by ambulatory BP monitoring during their pregnancies. We analyzed 1408 BP profiles obtained from 126 nulliparous and 109 multiparous pregnant women sampled for 48 consecutive h every 4 weeks from the first obstetric visit (usually within the first trimester of pregnancy) until delivery. Data were divided for comparative analysis according to parity (nulliparous versus multiparous), age (< or = 25, 26-30, 31-35, and > or = 36 yrs), and trimester of gestation. Circadian BP parameters established by population multiple-components analysis were compared between groups using a nonparametric test. A highly statistically significant circadian pattern described by a model that includes components with periods of 24 and 12h is demonstrated for systolic and diastolic BP for all groups of pregnant women in all trimesters (always p < 0.001). There was no significant difference in the 24h mean among groups divided by parity at any age or stage of pregnancy. A trend of increasing BP with age was found for diastolic but not for systolic BP. Although statistically significant, differences in the 24h mean of diastolic BP among groups divided by age were always less than 2 mm Hg. Data obtained from systematic ambulatory monitoring in normotensive pregnant women indicate the lack of differences in BP according to parity. The small, although significant, increase in diastolic BP with age may have scarce influence in the proper identification of women with gestational hypertension. Reference thresholds for BP to be used in the early identification of hypertensive complications in pregnancy could thus be developed as a function of the rest-activity cycle and gestational age only, and independently of parity or maternal age.