40 Assessing the association between BMI and blood pressures measured at alternative locations in obstetric patients


      In patients with obesity the distribution of subcutaneous tissue can make blood pressure (BP) measurements on the upper arm (UA) difficult. In these cases, alternative locations such as the wrist (WR) and forearm (FA) are commonly used. It is unknown if there is a discrepancy between these measurements for pregnant patients at extremes of body mass index (BMI). We hypothesize that BP measurements on the FA and WR will differ from the UA and this difference will be larger at greater BMIs.

      Study Design

      This is a prospective observational study of pregnant patients from July to August 2019. Study subjects had biometric measurements and 3 BP measurements (systolic BP – SBP and diastolic BP - DBP) taken at the UA, FA and WR. Measurements at the FA and WR were considered alternative locations and compared to the UA. Patients were stratified by BMI. Agreement among locations was assessed by Bland Altman analysis. Linear regression was used to assess the blood pressure discrepancy dependence on BMI.


      A total of 100 patients were included, 20 from each BMI class. Using Bland Altman plots, it was observed that BP measurements at each site correlated but were discrepant. For the FA, there was an upward bias of 11.5 mmHg (limits of agreement [LOA]: +30.7 to -7.8) for SBP and 11.2 mmHg (LOA:+25.9 to -2.9) for DBP as compared to the UA. For the WR, there was an upward bias of 7.1 mmHg (LOA: +35.1 to -20.9) for SBP and 7.3mmHg (LOA:+26.2 to -11.7) for DBP as compared to the UA. Overall, there was a larger discrepancy in BP measurements with increasing BMI. For the FA compared to the UA, the discrepancy of SBP increased by 0.43 mmHg (p<0.001) and of DBP increased by 0.18 mmHg (p=0.02) for each unit of BMI over 25. There was no statistically significant change in the discrepancy of SBP or DBP in the UA versus the WR measurements based on BMI.


      This study highlights that BP measurements are higher when taken at alternative locations, such as the WR and FA, and that FA BP measurements are higher than UA measurements with each BMI unit above 25.