The use of a set of new end points obtained from ambulatory blood pressure monitoring, in addition to the blood pressure values themselves, has been advocated to improve sensitivity and specificity in the diagnosis of hypertension and the evaluation of a patient's response to treatment. Among these parameters is the use of blood pressure load, the percentage of values above a given constant reference limit or computed by reference to daytime and nighttime limits. We examined the effectiveness of this parameter as a potential screening test for the detection of hypertension in pregnancy. We analyzed 2014 blood pressure series systematically sampled by ambulatory monitoring for 48 consecutive hours every 4 weeks from the first obstetric visit (usually within the first trimester of pregnancy) until delivery of 205 normotensive pregnant women and 123 women who developed gestational hypertension or preeclampsia. The blood pressure load was obtained as the percentage of values >140/110/90 mm Hg (systolic/mean arterial/diastolic blood pressure) during active hours or 120/95/80 mm Hg during resting hours, as well as by comparison with limits obtained by progressively reducing the previous limits by 5 mm Hg, up to a final threshold of 125/95/75 mm Hg (day) and 105/80/65 mm Hg (night). Sensitivity for the blood pressure load computed by reference to the highest limits used here is <55% in all trimesters of pregnancy. The best results were obtained when 130/100/80 mm Hg (day) and 110/85/70 mm Hg (night) were used as references in the third trimester, and when the lowest tested limits of 125/95/75 and 105/80/65 mm Hg were used as references in the first and second trimesters (sensitivity always >73%). The optimum reference limits for calculating the blood pressure load, markedly < mm Hg, must be defined as a function of gestational age, in keeping with the predictable trends in blood pressure along pregnancy previously documented.