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 were systematically studied by ambulatory blood pressure monitoring during their pregnancies. We analyzed 1254 blood pressure series sampled for 48 consecutive hours every 4 weeks from the first obstetric visit (usually within the first trimester of pregnancy) until delivery in 205 normotensive pregnant women. Data were divided for comparative analysis by parity (nulliparous versus multiparous), age (</=25, 26 to 30, 31 to 35, and >/=36 years), and trimester of gestation. Circadian parameters established by population multiple-component analysis were compared between groups with a nonparametric test. Effects of age and parity on blood pressure 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 blood pressure 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>0.160). A trend of increasing blood pressure with age was found for diastolic but not systolic blood pressure. Although statistically significant, differences in the 24-hour mean of diastolic blood pressure among groups divided by age were always <1.5 mm Hg. Data obtained from systematic ambulatory monitoring in normotensive pregnant women indicate the lack of differences in blood pressure according to parity. The small, although significant, increase in diastolic blood pressure with age may have little influence in the proper identification of women with gestational hypertension. Reference thresholds for blood pressure to be used in the early identification of hypertensive complications in pregnancy could thus be developed as a function of rest-activity cycle and gestational age, independent of parity or maternal age.