The white coat effect in hypertensive pregnancy: much ado about nothing?

OBJECTIVES: To determine the prevalence of white coat hypertension and white coat effect among hypertensive pregnant women and to assess whether the presence of a significant white coat effect was associated with adverse pregnancy outcome when clinical management was based upon standard sphygmomanometric blood pressure recordings.

DESIGN: Prospective blinded studies assessing the presence of a white coat effect.

SETTING: Antenatal ward and pregnancy day assessment unit of St George Hospital, a teaching hospital in Sydney, Australia.

POPULATION: One hundred and twenty-one hypertensive pregnant women in the second half of their pregnancy admitted to hospital or the day assessment unit for management of their hypertensive disorders.

METHODS: Routine sphygmomanometric blood pressures were recorded by midwives in the ward or day assessment unit and awake blood pressure recordings were averaged. These blood pressures were compared with average awake blood pressures recorded by ambulatory blood pressure monitor (ABPM) (Spacelabs 90207, Seattle, Washington, USA). White coat hypertension was defined as an average sphygmomanometer blood pressure > or = 140 mmHg systolic and/or > or = 90 mmHg diastolic with awake ABPM average blood pressure within the normal range for ABPM-derived blood pressures in pregnancy, according to gestation. White coat effect was the difference between average sphygmomanometer blood pressure and average awake ABPM-derived blood pressure. All clinical management was based upon routine sphygmomanometer recordings and clinicians were blinded to ABPM data.

MAIN OUTCOME MEASURES: Prevalence of white coat hypertension and white coat effect; maternal and fetal outcomes in those with and without a white coat effect of > or = 20 mmHg systolic and/or > or = 10 mmHg diastolic.

RESULTS: Systolic and diastolic white coat hypertension were present in only 3.2% and 4.2% of the group, respectively. A systolic white coat effect > or = 20 mmHg was found in only 4.2% but 20.2% (26% for day assessment unit patients vs 15% for inpatients; P = 0.17) had a diastolic white coat effect > or = 10 mmHg. There was no difference in maternal or fetal outcomes between women with and without a white coat effect.

CONCLUSIONS: White coat hypertension is an infrequent occurrence in mildly hypertensive pregnant women. Although a white coat effect is present more often, this is associated with clinical outcomes similar to women who do not exhibit this phenomenon. Using ABPM to identify a white coat effect in women presenting with hypertension in the second half of their pregnancy does not appear to be clinically useful.