Impact of obesity on blood pressures measured at alternative locations during pregnancy

In patients with obesity, the distribution of subcutaneous tissue can make blood pressure measurement on the standard location of the upper arm difficult. In these cases, alternative locations, such as the lower arm or wrist, are commonly used. It is unknown whether there is a discrepancy in these measurements for pregnant patients at extremes of body mass index.

We hypothesized that noninvasive blood pressure measurements on the lower arm and wrist will differ from blood pressure measurements on the upper arm and that this difference will be greater with increasing body mass index.

We conducted a prospective observational study of pregnant patients from July 2020 to August 2020. We collected study subjects' biometric measurements and took 3 blood pressure measurements (systolic and diastolic blood pressures) from the upper arm, lower arm, and wrist. Measurements on the lower arm and wrist were considered alternative locations and compared with measurements on the upper arm. We stratified patients by body mass index. Agreement between locations was assessed using the Bland-Altman analysis. We used linear regression to assess the blood pressure discrepancy dependence on body mass index.

We included 100 patients with 20 patients from each body mass index class. Blood pressure measurements at each site correlated but were discrepant. For the lower arm, there was an upward bias of 11.5 mm Hg (limit of agreement, +30.7 to -7.8) for systolic blood pressure and 11.2 mm Hg (limit of agreement, +25.9 to -2.9) for diastolic blood pressure compared with the upper arm. For the wrist, there was an upward bias of 7.1 mm Hg (limit of agreement, +35.1 to -20.9) for systolic blood pressure and 7.3 mm Hg (limit of agreement, +26.2 to -11.7) for diastolic blood pressure compared with the upper arm. Overall, there was a greater discrepancy in blood pressure measurements between the lower and upper arms with increasing body mass index. When comparing blood pressure measurements between the lower and upper arms, the discrepancy increased by 0.43 mm Hg (P<.001) for systolic blood pressure and 0.18 mm Hg (P=.02) for diastolic blood pressure with each increasing body mass index unit. There was no statistically significant change in the discrepancy of systolic (P=.45) or diastolic (P=.86) blood pressure in the upper arm vs the wrist based on body mass index.

This study highlighted that blood pressure measurements are higher when taken at alternative locations, such as the lower arm and wrist, and that lower arm blood pressure measurements are increasingly discrepant from upper arm blood pressure measurements with increasing body mass index.