Accepted for/Published in: JMIR mHealth and uHealth
Date Submitted: Mar 1, 2025
Open Peer Review Period: Mar 1, 2025 - Apr 26, 2025
Date Accepted: Dec 1, 2025
(closed for review but you can still tweet)
Terminal Digit Preference and Threshold Avoidance in Digital Blood Pressure Measurements During Pregnancy: Insights from the CLIP and PRECISE Cohorts
ABSTRACT
Background:
Screening for, detecting, and managing pregnancy hypertension is a core function of antenatal care. To reduce both training requirements and the risks of measurement error in blood pressure (BP) values, automated and semi-automated BP devices have been validated in normotensive and hypertensive pregnant women, and introduced for serial antenatal measurement of BP.
Objective:
We aimed to (i) determine whether or not repeated blood pressure measurements reduced the presence of terminal digit preference; and (ii) discern whether or not there was evidence of threshold avoidance in the Community-Level Interventions for Pre-eclampsia (CLIP) trials compared with the purely observational PREgnancy Care Integrating translational Science, Everywhere (PRECISE) cohorts.
Methods:
The BP 3AS1-2 and CRADLE VSA low-cost Microlife BP devices were used by trained research staff in the CLIP trials conducted in India, Mozambique, Nigeria (pilot trial only), and Pakistan, and the PRECISEcohorts of unselected pregnant women and non-pregnant women of reproductive age recruited in The Gambia, Kenya, and Mozambique. Both devices algorithmically calculate systolic (sBP) and diastolic (dBP) values displayed on digital read-outs. All BP readings were entered manually into a digital platform, which averaged them as the BP for that visit; the first and second readings were averaged unless they were more than 10 mmHg different, which triggered a third reading and the second and third readings were averaged.
Results:
51,875 participants had their BP measured 438,404 times. Using raw BP values, there was terminal digit preference (of 911,500 values, 129,539 [14.2% vs 10.0%; p<0.001] values ended in a ‘0’). 28,929 (6.6%) of 437,446 dBP values were 62mmHg, compared with 9310 (4.8%) of 195,349 from the averaged values (p<0.001); errors obviated by averaging BP values. There was evidence of both threshold preference and avoidance in the CLIP trials and the PRECISE cohort.
Conclusions:
Given the excess of 62 mmHg values, there is a shared inherent algorithmic error in the calculation of dBP in the BP 3AS1-2 and CRADLE VSA devices. Averaged BP measurements are important to reduce the impact of user errors in manually recording blood pressure values. We recommend that automated and semi-automated BP devices include Bluetooth functionality to automatically transfer readings to digital health records to further optimise care. Clinical Trial: NCT01911494
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