Prospective evaluation of the tolerance-hyperbaric test for the early identification of hypertensive complications in pregnancy

We have examined prospectively whether the tolerance-hyperbaric test (THT), combined approach of establishing tolerance intervals for the circadian variability of blood pressure (BP) as a function of gestational age, and then computing the hyperbaric index (HBI, area of BP excess above the upper limit of the interval) by comparison of any patient's BP profile with those intervals, provides high sensitivity for the early identification of pregnant women who subsequently will develop hypertensive complications in pregnancy. We analyzed 2,014 BP series obtained from 176 women with uncomplicated pregnancies and 121 women who developed gestational hypertension or preeclampsia (gestational hypertension and proteinuria, above 300 mg/24 hours in urine). BP was sampled at half-hour intervals during the day and hourly during the night for 48 hours with an ABPM-630 Colin device once every 4 weeks from the first visit to the hospital (mostly before 14 weeks of gestation) until delivery. Circadian 90% tolerance limits for BP were computed as a function of trimester of gestation from 497 series previously sampled from a reference group of 189 normotensive pregnant women [Hermida RC, et al. J Perinat Med 1997;25:237–253]. Sensitivity of the THT was 91% for women sampled during the first trimester of gestation, and increased up to 99% in the third trimester. Specificity for a threshold HBI value for diagnosis of 15 mmHgXhour obtained from previous studies [Hermida RC, et al. Hypertension 1998;31:83–88] was above 99% in all trimesters. The positive and negative predictive values were above 95% in all trimesters. The test provided, on the average, an early identification of gestational hypertension and preeclampsia 23 weeks prior to the clinical confirmation of the disease. The THT, now validated prospectively in women systematically sampled by ambulatory monitoring throughout pregnancy, represents a reproducible, noninvasive, and high sensitivity test for the very early identification of subsequent gestational hypertension and preeclampsia.