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The evaluation of predictable variability in blood pressure by the use of ambulatory devices, and the proper processing of the time series thus obtained, can be useful for the early assessment of hypertensive complications in pregnancy. We have used this approach to quantify a predictable pattern of blood pressure and heart rate throughout pregnancy in clinically healthy women as well as in pregnant women who developed gestational hypertension or preeclampsia. We analyzed 503 blood pressure series from 71 healthy pregnant women and 256 series from 42 women who developed gestational hypertension or preeclampsia. Blood pressure monitoring (48-hour) was done once every 4 weeks after the first obstetric consultation. 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. This method 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 21st week of pregnancy, followed by an increase in blood pressure up to the day of delivery. This pattern of variation is not found in pregnancies complicated with gestational hypertension or even preeclampsia: the 24-hour mean of blood pressure is stable until the 22nd week of pregnancy and then correlated with gestational age, indicating a significant linear increase of blood pressure in the second half of pregnancy. For both healthy and complicated pregnancies, heart rate slightly increases until the end of the second trimester, and it is stable thereafter. 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 end points for an early identification of gestational hypertension and preeclampsia.