Comparison of clinic and home blood pressure readings in higher risk pregnancies – Secondary analysis of the BUMP 1 trial

Objective: To compare clinic and home blood pressure readings in higher risk pregnancies in the antenatal period from 20 weeks gestation, and to evaluate differences between the two modalities. Study design: A cohort study comprising a secondary analysis of a large randomised controlled trial (BUMP 1). Population: Normotensive women at higher risk of pregnancy hypertension randomised to self-monitoring of blood pressure. Main outcome measures: The primary outcome was the overall mean difference between clinic and home readings for systolic blood pressure (sBP) and diastolic blood pressure (dBP). Blood pressure readings were averaged across each gestational week for each participant and compared within the same gestational week. Calculations of the overall differences were based on the average difference for each week for each participant. Results: The cohort comprised 925 participants. In total, 92 (10 %) developed a hypertensive disorder during the pregnancy. A significant difference in the overall mean sBP (clinic – home) of 1.1 mmHg (0.5–1.6 95 %CI) was noted, whereas no significant difference for the overall mean dBP was found (0.0 mmHg (−0.4–0.4 95 %CI)). No tendency of proportional bias was noted based on Bland-Altman plots. Increasing body mass index in general increased the difference (clinic – home) for both sBP and dBP in a multivariate analysis. Conclusions: No clinically significant difference was found between clinic and home blood pressure readings in normotensive higher risk pregnancies from gestational week 20+0 until 40+0. Clinic and home blood pressure readings might be considered equal during pregnancy in women who are normotensive at baseline.