Influence of parity and age on ambulatory monitored blood pressure during pregnancy

Studies based on casual lood pressure (BP) values concluded that both age and parity have significant effects on BP during pregnancy. We have tested these results on clinically healthy normotensive women who were systematically sampled by ambulatory BP monitoring (ABPM) during their pregnancies. We analyzed 1404 BP series sampled from 234 normotensive pregnant women. BP was measured every 20 minutes during the day and every 30 minutes during the night for 48 hours with an ambulatory device once every 4 weeks from the first visit to the hospital (usually within the first trimester of gestation) until delivery. Data were divided for comparative analysis according to parity (nullipara vs multipara), age (≤25, 26-30, 31-35, and ≥35 years), and trimester of gestation. Circadian parameters established by population multiple-components analysis [Fernández & Hermida. Chronobiol Int 1998;15:191-204] were compared between groups with a nonparametric test. Effects of age and parity upon BP were also tested by ANOVA. A highly statistically significant circadian pattern described by a model that includes components with periods of 24 and 12 hours 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 24-hour mean among groups divided by parity at any age or stage of pregnancy (always P>0.228). A trend of increasing BP with age was found for diastolic but not for systolic BP. Although statistically significant, differences in the 24-hour mean of diastolic BP among groups divided by age were always below 1.5 mm Hg. Data obtained from systematic ABPM 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 [Hermida et al. Hypertension 1998;31:83-89] could thus be developed as a function of rest-activity cycle and gestational age only, independently of parity or chronological age.