Second trimester ambulatory blood pressure in nulliparous pregnancy: a useful screening test for pre-eclampsia?

To assess the effectiveness of second trimester 24-hour ambulatory blood pressure measurement as a screening test for pre-eclampsia.

Prospective interventional study.

John Radcliffe Maternity Hospital, Oxford, and Queen Charlotte's and Chelsea Hospital, London.

One hundred and sixty-two normotensive nulliparous women recruited at hospital booking clinics.

Ambulatory blood pressure was measured at 18 and 28 weeks gestation using the TM2420 monitor.

The development of pre-eclampsia.

Awake systolic and mean arterial pressures were significantly increased (P < 0.02) at 18 weeks in those who later developed pre-eclampsia. Those differences were more apparent at 28 weeks at which time the diastolic pressure was also increased (P < 0.01). At both stages of gestation the higher readings were sustained during sleep so that the awake-sleep differences were similar in relation to each outcome. The group with incipient pre-eclampsia had a significantly faster heart rate at both 18 and 28 weeks (P < 0.002) The sensitivity in predicting pre-eclampsia for a mean arterial pressure of 85 mmHg or greater at 28 weeks was 65%, with a positive predictive value of 31%. The sensitivity and positive predictive value for a test combining a mean arterial pressure of 85 mmHg or greater and a heart rate of 90 bpm or greater were 53% and 45%, respectively.

Although second trimester ambulatory blood pressure is significantly increased in women who later develop pre-eclampsia, the predictive values for blood pressure alone are low. The efficiency of the test is increased by combining the awake ambulatory heart rate and blood pressure measurement together. If an effective method for preventing pre-eclampsia becomes available (commencing at 28 weeks gestation), then awake ambulatory blood pressure and heart rate may have some clinical value as a screening test.