Thresholds for Ambulatory Blood Pressure Monitoring Based on Maternal and Neonatal Outcomes in Late Pregnancy in a Southern Chinese Population

BACKGROUND: In contrast to the general population, outcome‐derived thresholds for diagnosing ambulatory hypertension in pregnancy are not yet available. We aimed to identify and compare outcome‐derived ambulatory blood pressure (BP) monitoring thresholds for adverse perinatal outcomes by using approaches related and not related to clinic BP in a southern Chinese population. METHODS AND RESULTS: Ambulatory BP monitoring was performed in a cohort of 1768 high‐risk participants in late pregnancy who were not taking antihypertensive medications. Participants were followed for composite maternal (severe complications) and neonatal (pregnancy loss, advanced neonatal care, and small for gestational age) outcomes. Modeling of clinic BP–unrelated approaches revealed a nonlinear threshold effect of ambulatory diastolic BP on the composite outcome, with increased risk for daytime ≥79 mm Hg and 24‐hour measurement ≥76 mm Hg. For other ambulatory BP components showing linear associations with outcome, the following thresholds were identified: 131 mm Hg for daytime systolic, 121 mm Hg for nighttime systolic, 130 mm Hg for 24‐hour systolic, and 73 mm Hg for night‐time diastolic BP. These thresholds unrelated to clinic BP were lower than the equivalents yielding a similar probability of outcome to clinic BP of 140/90 mm Hg and were comparable with equivalents to clinic BP of 130/80 mm Hg. CONCLUSIONS: Using an outcome‐derived approach unrelated to clinic BP, we identified rounded thresholds to define ambulatory hypertension in at‐risk women in late pregnancy in a southern Chinese population as follows: 130/80 mm Hg for daytime, 120/75 mm Hg for nighttime, and 130/75 mm Hg for 24‐hour measurement. For wider clinical applicability and to align both nonpregnancy and pregnancy ambulatory BP monitoring with an outcomes‐based approach, prospective, multiethnic, international studies from early pregnancy onward will be required.