Objective: To assess the role of 24-hour ambulatory blood pressure measurement in the mid-second trimester as a predictive test for the development of hypertension in pregnancy.
Design: Prospective intervention.
Setting: The Rotunda Hospital, Dublin.
Participants: One thousand one hundred and two healthy primigravid women.
Intervention: 24-hour ambulatory blood pressure measurement at 18 to 24 weeks of gestation.
Main outcome measures: The development of pre-eclampsia or gestational hypertension.
Results: A total of 1048 women had sufficient readings to be included in the final analysis. Of these, 23 (2.2%) developed pre-eclampsia, 64 (6.1%) developed gestational hypertension and 961 (91.7%) remained normotensive. Significantly higher ambulatory blood pressures were recorded in both the pre-eclamptic and gestational hypertensive group compared with the normotensive group. In addition, the gestational hypertensive group had significantly higher clinically measured blood pressure compared with the normotensive group. There were no differences between the pre-eclamptic and the gestational hypertensive group for any of the blood pressure parameters analysed. The best overall predictor for pre-eclampsia was 24-hour mean diastolic pressure which using a cutoff level of 71 mmHg gave a test with a sensitivity of only 22% and a positive predictive value of 15%.
Conclusion: Because the absolute differences are small and the overlap between the hypertensive and normotensive groups large, ambulatory blood pressure measurement, in a healthy primigravid population, between 18 and 24 weeks of gestation is not a useful predictor of hypertension.