The evaluation of predictable variability in blood pressure and heart rate by (a) the use of fully ambulatory devices, and (b) the proper processing of the time series thus obtained, can be useful in assessing early cardiovascular disease risk in pregnancy. We have used this approach to quantify a predictable time structure of blood pressure throughout pregnancy in clinically healthy women as well as in pregnant women who developed gestational hypertension of preeclampsia. We analyzed a total of 745 blood pressure series sampled by ambulatory monitoring for about 48 hours in each of several occasions in 189 women with uncomplicated pregnancies, 71 with gestational hypertension, and 29 with preeclampsia. The pattern of variation along gestation of the 24-hour mean of blood pressure for groups of normotensive and hypertensive pregnant women was established by polynomial regression analysis. Regression analysis revealed predictable patterns of variation of 24-hour means with gestational age: for normotensive pregnant women, results indicate a steady decrease in blood pressure up to the 20th week of pregnancy, followed by an increase in blood pressure up to the day of delivery. Women with gestational hypertension or preeclampsia are characterized, however, by a continuous linear increase of blood pressure with gestational age, starting from the beginning of pregnancy. This study confirms and extends to ambulatory everyday life conditions the predictable pregnancy-associated variability in blood pressure. The differences between uncomplicated and complicated pregnancies offer new endpoints for an early identification of gestational hypertension and preeclampsia.