Choosing blood pressure thresholds to inform pregnancy care in the community: An analysis of cluster trials

Objective: To inform digital health design by evaluating diagnostic test properties of antenatal blood pressure (BP) outputs and levels to identify women at risk of adverse outcomes. Design: Planned secondary analysis of cluster randomised trials. Setting: India, Pakistan, Mozambique. Population: Women with in-community BP measurements and known pregnancy outcomes. Methods: Blood pressure was defined by its outputs (systolic and/or diastolic, systolic only, diastolic only or mean arterial pressure [calculated]) and level: normotension-1 (<135/85 mmHg), normotension-2 (135–139/85–89 mmHg), non-severe hypertension (140–149/90–99 mmHg; 150–154/100–104 mmHg; 155–159/105–109 mmHg) and severe hypertension (≥160/110 mmHg). Dose–response (adjusted risk ratio [aRR]) and diagnostic test properties (negative [−LR] and positive [+LR] likelihood ratios) were estimated. Main Outcome Measures: Maternal/perinatal composites of mortality/morbidity. Results: Among 21 069 pregnancies, different BP outputs had similar aRR, −LR, and +LR for adverse outcomes. No BP level (even normotension-1) was associated with low risk (all −LR ≥0.20). Across outcomes, risks rose progressively with higher BP levels above normotension-1. For each of maternal central nervous system events and stillbirth, BP ≥155/105 mmHg showed at least good diagnostic test performance (+LR ≥5.0) and BP ≥135/85 mmHg at least fair performance, similar to BP ≥140/90 mmHg (+LR 2.0–4.99). Conclusions: In the community, normal BP values do not provide reassurance about subsequent adverse outcomes. Given the similar performance of BP cut-offs of 135/85 and 140/90 mmHg for hypertension, and 155/105 and 160/110 mmHg for severe hypertension, digital decision support for women in the community should consider using these lower thresholds.