Results
Phase 1: Performance evaluation of the CDXP and Omron M6 Comfort
Of the approached 68 women 34 were willing to participate and met the inclusion criteria as described above. Participant details of this phase are shown in Table 3. A total of 33 complete measurements with the CDXP, Omron M6 Comfort and the aneroid manometer were conducted. 1 Participant was excluded in the comparison of the CDXP due to the inability to refrain from moving the arm.
The mean aneroid recruitment SBP was 113 mmHg (93-147 mmHg), the mean DPB was 73 mmHg (59-99 mmHg). We did not detect any difference in SBP and DBP between the aneroid meter and CDXP: -0.7±6.5 mmHg (p=0.38) and 0.4±5.7 mmHg (p=0.55) for SBP and DBP respectively. The aneroid manometer measured SBP mmHg significantly higher (1.5±5.8 (p=0.04)) and DBP lower (-2.8±5.8 mmHg (p<0.01)) as compared to the Omron M6 Comfort. Using an univariate regression analysis we did not find a difference between measurements in round 1 and 2 and we could not explain the differences in blood pressure measurements between the Omron M6 Comfort and the aneroid manometer by body mass index, gestational age, upper arm or wrist circumference.
Figure 1 and 2 illustrate Bland-Altman plots of both the CDXP and Omron M6 Comfort and shows that there is no indication of a systematic relation between the blood pressure ranges and the performance of the two devices.
Phase 2: Home CDXP versus office blood pressure measurement
Of the 64 approached women 32 were willing to participate and met the inclusion criteria as described above. 3 Women accidently measured their home measurement on a different day as their hospital measurement and were excluded from statistical analyses. Participant details of this phase are shown in Table 3.
The mean blood pressure values and the mean differences between measurements are listed in Table 4. In 7 patients the home blood pressure measurements were not complete due to technical problems (n=3), simply forgetting (n=3) and going into labor during the measurements (n=1). Their available partial data were incorporated in the analysis. Comparison showed that for both CDXP self-measurements the SBP, but not the DBP, was significantly lower than the standard office measurement. The second measurement of the office self-measurement was slightly significantly lower than the first measurement. This was not observed in home self-measurement. The found significant differences in office SBP and home SBP was not correlated with age, amenorrhea duration, BMI before and during pregnancy, parity, wrist and upper mid arm circumference, pulse rate and the range of blood pressure (data not shown).
Evaluation of the home self-measurements with the CDXP during the day showed that there were small differences between the first and second home self-measurement at the different time points in both SBP (maximum of 2.3±4.6 mmHg) and DBP (maximum of 2.1±3.1 mmHg). Figure 3 shows the mean standard office measurement and mean first home self-measurements of SBP and DBP over the different time points. The standard office measurement of SBP was significantly higher as compared to all time points of the home self-measurement: morning 6.7±10.5 mmHg, noon 7.6±9.7 mmHg, afternoon 7.6±10.7 mmHg, night 7.2±11.9 mmHg. We did not detect any difference in DBP between the standard office measurement and the home self-measurement time points.
Table 5 shows the mean scores to the patients’ experience questionnaire. Two patients did not fill out the questionnaire and two patients left one question blank and were therefore excluded from analysis. The mean SUS-score was 85%, corresponding with an excellent score. Most women indicated that they managed to follow all the instructions and that they trusted their measured blood pressure. The vast majority thought that home monitoring of the blood pressure is a good idea and a good option for replacement of the standard office measurement. Most women liked the idea of having less hospital visits due to home monitoring, while only 3% disagreed. Women reported that they rather not miss listening to the fetal heart. Patients also reported that they liked the idea of home monitoring of the blood pressure even more if the course of pregnancy led to extra hospital visits for blood pressure measurement only.