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

Studies based on casual blood pressure measurements concluded that both age and parity have significant effects on blood pressure during pregnancy. We have tested these results on clinically healthy normotensive women who wer e systematically studied by ambulatory blood pressure monitoring during the ir pregnancies. We analyzed 1254 blood pressure series sampled for 48 conse cutive hours every 4 weeks from the first obstetric visit (usually within t he first trimester of pregnancy) until delivery in 205 normotensive pregnan t women. Data were divided for comparative analysis by parity (nulliparous versus multiparous), age (less than or equal to 25, 26 to 30, 31 to 35, and greater than or equal to 36 years), and trimester of gestation. Circadian parameters established by population multiple-component analysis were compa red between groups with a nonparametric test. Effects of age and parity on blood pressure were also tested by ANOVA. A highly statistically significan t circadian pattern described by a model that includes components with peri ods of 24 and 12 hours is demonstrated for systolic and diastolic blood pre ssure 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 b y parity at any age or stage of pregnancy (always P >0.160). A trend of inc reasing blood pressure with age was found for diastolic but not systolic bl ood pressure. Although statistically significant, differences in the 24-hou r mean of diastolic blood pressure among groups divided by age were always <1.5 mm Hg. Data obtained from systematic ambulatory monitoring in normoten sive pregnant women indicate the lack of differences in blood pressure acco rding to parity. The small, although significant, increase in diastolic blo od pressure with age may have little influence in the proper identification of women with gestational hypertension. Reference thresholds for blood pre ssure to be used in the early identification of hypertensive complications in pregnancy could thus be developed as a function of rest-activity cycle a nd gestational age, independent of parity or maternal age.