Nighttime aspirin, BP test target preeclampsia

OB/GYN News, Nov 1, 2002 by Heidi Splete

New studies support two innovative strategies in the war against preeclampsia--the tolerance-hyperbaric test and low-dose aspirin taken at night.

The tolerance-hyperbaric test (THT) can be used as early as the first trimester to identify up to 93% of pregnant women who will develop blood pressure complications months before they have symptoms that standard tests can detect, said Ramon C. Hermida, Ph.D., of the University of Vigo (Spain).

A second study, also conducted by Dr. Hermida and his associates, included 341 women at high risk for preeclampsia. In that study, only 1.7% of those who took low-dose aspirin at bedtime later developed preeclampsia, compared with 14% of those women who took a placebo--a significant difference, he said.

In the first study, which included 403 women, the THT was used to compare a pregnant patient's blood pressure changes over a 48-hour period with the expected variability of blood pressure due to natural circadian rhythms. Patients whose readings were consistently outside the expected range were flagged.

Study participants wore a portable blood pressure cuff and monitor to record the readings.

The investigators analyzed data from 2,430 blood pressure series sampled by ambulatory blood pressure monitoring for 48 hours once every 4 weeks from the first obstetric visit until delivery.

A total of 168 women ultimately developed gestational hypertension or preeclampsia, and 235 had uncomplicated pregnancies.

Sensitivity of the THT was 93% for tests conducted during the first trimester and increased up to 99% in the third trimester. Specificity was above 98% in all trimesters. The positive and negative predictive values were above 96% in all trimesters, he reported.

"Given its high sensitivity and specificity, we believe all pregnant women should have the tests performed at least once, preferably within the first trimester," Dr. Hermida said in an interview.

In an interview, Dr. Rosemarie Robertson, past president of the American Heart Association, praised the study. "This is a very clever thing to do in keeping with what we know about hypertension. You're assessing the hypertensive burden and using it to predict something later on," she said.

Although the test has great promise, it must be studied in larger sets of women, with cost effectiveness taken into consideration, added Dr. Robertson, professor of medicine at Vanderbilt University, Nashville, Tenn.

Many hospitals have portable blood pressure monitoring equipment, but it has not been widely used to predict preeclampsia. It may become more widely used in conjunction with Dr. Hermida's software, which determines whether a woman's 48-hour blood pressure variations are consistently outside the normal range. The software will be available to physicians later this fall, Dr. Hermida said.

In the second study, low-dose aspirin taken before bedtime significantly reduced the incidence of preeclampsia in women at high risk for the disorder due to obesity or history of miscarriage or gestational high blood pressure.

The double-blind, randomized, controlled trial included 34l women divided into six groups. Each group received either 100 mg of aspirin or a placebo at one of three times--on awakening, 8 hours after awakening, or bedtime.

Only 1.7% of the women who took low-dose aspirin at bedtime had preeclampsia, compared with 14% of those who took a placebo. Aspirin taken upon awakening was not associated with a significant reduction in blood pressure, compared with placebo. A blood pressure reduction was highly statistically significant when aspirin was given 8 hours after awakening and, to a greater extent, when it was taken at bedtime, Dr. Hermida said.

Taking low-dose aspirin at bedtime also was associated with a reduced incidence of gestational hypertension, compared with placebo (6.8% vs. 30.4%) and intrauterine growth retardation (3.4% vs. 16.1%).

In addition, none of the women who took low-dose aspirin at bedtime delivered preterm, and their babies weighed an average of 250 g more than those born to women on placebo or those who took low-dose aspirin in the morning.

The study findings contradicts previous research showing that low-dose aspirin has little or no ability to prevent preeclampsia no matter when it's taken.

A previous study by Dr. Hermida and colleagues summarized additional research on how aspirin's effects varied depending on when it was taken (Hypertension 34[4, part 2]:1016-23, 1999). Aspirin's lack of effectiveness in preventing preeclampsia in previous studies could be due to several factors, including the initiation of low-dose aspirin after 16 weeks' gestation, the use of doses less than 80 mg/day that don't affect placental thromboxane, and failure to time aspirin administration to match circadian rhythms, the researchers said.

It's not clear why time of aspirin administration makes a difference in preventing preeclampsia, Dr. Robertson added.