Are nocturnal home and ambulatory blood pressure measurements clinically interchangeable during high-risk pregnancy?

Nocturnal blood pressure is a strong predictor of adverse maternal-fetal outcomes, particularly preeclampsia. While 24-h ambulatory blood pressure monitoring (ABPM) is the reference method for nocturnal blood pressure assessment, home blood pressure monitoring (HBPM) devices capable of nocturnal measurements have recently emerged. However, their comparability and clinical interchangeability during pregnancy remain unclear. High-risk pregnant women underwent both nocturnal HBPM and 24-h ABPM. Nocturnal systolic (SBP) and diastolic blood pressure (DBP) values were compared using paired analyses, correlation coefficients, Bland-Altman agreement, intraclass correlation coefficients (ICC), and categorical agreement for nocturnal hypertension. Mean nocturnal SBP and DBP were similar between HBPM and ABPM (SBP: 103 ± 10.2 vs 104 ± 11.1 mmHg, p = 0.139; DBP: 61 ± 7.3 vs 60 ± 7.0 mmHg, p = 0.808). Correlations were moderate for both SBP (r = 0.63) and DBP (r = 0.60). Bland-Altman analysis showed wide limits of agreement (approximately ±17 mmHg for SBP and ± 12 mmHg for DBP), with 39% and 35% of patients, respectively, exhibiting inter-method differences >5 mmHg. ICC values indicated moderate agreement (SBP ICC = 0.57-0.63; DBP ICC = 0.60). Diagnostic concordance for nocturnal hypertension was moderate (Kappa = 0.47). Despite similar population-level nocturnal blood pressure means, HBPM and ABPM are not clinically interchangeable in high-risk pregnancy. Nocturnal HBPM may provide complementary clinical information, warranting further prognostic evaluation.