Out-of-office blood pressure measurement for the diagnosis of hypertension in pregnancy: Survey of Canadian Obstetric Medicine and Maternal Fetal Medicine specialists

Short abstract

Background

Multiple hypertension guidelines recommend out-of-office measurements for the diagnosis of hypertension in non-pregnant adults, whereas pregnancy guidelines recommend in-office blood pressure measurements. The objective of our study was to determine how Canadian Obstetric Medicine and Maternal Fetal Medicine specialists measure blood pressure in pregnancy.

Methods

An email survey was sent to 69 Canadian Obstetric Medicine and Maternal Fetal Medicine specialists in academic centers across Canada to explore the practice patterns of blood pressure measurement in pregnant women.

Results

The response rate was 48%. The majority of respondents (63.6%) preferred office blood pressure measurement for diagnosing hypertension, but relied on home blood pressure readings for ongoing monitoring and management of hypertension during pregnancy (59.4%). The preferred method of out-of-office blood pressure measurement was home monitoring; 24-hour ambulatory blood pressure monitoring was not used due to limited availability and cost.

Conclusions

There is wide practice variation in methods of measuring blood pressure among Canadian specialists managing hypertension in pregnancy.

Introduction

Accurate blood pressure (BP) measurement is important for the diagnosis of hypertension and should be performed both in-office and out-of-office.¹ Hypertension Canada and other international guidelines and organizations recommend out-of-office measurements for diagnosis of hypertension, using 24-hour ambulatory blood pressure measurement (ABPM) or home BP measurements.^2–5 Both types of measurements are predictors of cardiovascular outcomes and target end organ damage and enable the identification of white coat hypertension (WCH) and masked hypertension.²

Hypertensive disorders of pregnancy are a common cause of maternal, fetal, and neonatal morbidity and mortality, affecting approximately 5–10% of all pregnancies.⁶ Currently, hypertensive disorders of pregnancy are diagnosed after an in-office systolic blood pressure (SBP) reading of ≥140 mm Hg or a diastolic blood pressure (DBP) reading of ≥90 mm Hg, based on average of at least two measurements taken at least 15 minutes apart.⁷ Recommendations for pharmacological management of hypertension during pregnancy are similarly based on BP measurement obtained in-office.⁸

In many centers across Canada, Obstetric Internists (General Internal Medicine specialists or subspecialists with additional training in Obstetric Medicine) and Maternal Fetal Medicine (MFM) specialists are the medical care providers most responsible for the care of pregnant women with hypertension.⁹ Both Hypertension Canada and Society of Obstetricians and Gynaecologists of Canada (SOGC) guidelines are widely available and are disseminated to general internists and specialists across the country to help manage hypertension both in non-pregnant and pregnant population, respectively.

Given the wide practice variation in BP measurement methodology in the guidelines between pregnant and non-pregnant women, we sought to understand how front-line care providers measure BP in pregnant women who are at high risk of developing hypertension in pregnancy. We designed and distributed a survey to determine the current practice patterns of Obstetric Medicine (ObM) and MFM specialists surrounding the use of in-office versus out-of-office BP measurement in pregnant women for the purpose of diagnosis and management of hypertension.

Methods

An online survey was disseminated between 6 September 2016 and 30 September 2016 using FluidSurveys Online Software. Participants were identified by study investigators who had knowledge of ObM specialists at each major obstetric academic center across Canada. This list was generated first by ensuring that a major obstetric center in each province was represented. The ObM internist(s) known to practice at the center was then invited to participate. If ObM was not available at that obstetric center, then MFM specialists at that center were contacted. Academic centers in Canada include major maternity centers, which are teaching centers affiliated with universities. Three email reminders were sent to all participants at 1, 2, and 4 weeks after the invitation to improve response rates. Informed consent was obtained from the participants. Ethics was obtained from the University of British Columbia Research Ethics Board.

Survey instrument

The authors jointly developed the questionnaire, which was piloted by local obstetricians and ObM colleagues prior to dissemination of the survey. The survey (Supplementary Appendix 1) included both physician demographic and practice information. Participants were specifically asked about preferred BP measurement modality to diagnose and monitor hypertensive disorders of pregnancy, as well as how BP was measured in-office and out-of-office.

Descriptive statistics were used to analyze categorical data. Responses to open-ended questions were coded and categorized for emerging themes. Statistical analysis was performed using R.¹⁰

Results

Surveys were sent to 72 physicians (44 were ObM, and 28 were MFM); however, three email addresses were incorrect and the physician could not be contacted. Of the 69 physicians contacted, there were 33 respondents (response rate was 48%). The baseline characteristics of the respondents are shown in Table 1. Most of the physicians who responded were ObM. Respondents were predominately from Western Canada and Quebec, with no respondents from the Maritimes. Overall, the respondents had a diverse range of clinical experience with 21% having more than 20 years of experience.

Table 1.

Characteristics of survey respondents.

Characteristic	N (%)
Specialty
ObM	23 (69.7)
MFM	10 (30.3)
Location
Western Canada	17 (51.5)
Ontario	6 (18.2)
Quebec	10 (30.3)
Maritimes	0 (0)
Clinical practice
Academic	13 (39.4)
Mixed	2 (54.5)
Community	18 (6.1)
Number of deliveries performed annually at center of practice
<2500	3 (9.1)
2500–5000	17 (51.5)
>5000	13 (39.4)
Number of new patients with HDP seen per month
0–5	5 (15.2)
5–10	18 (54.5)
10–15	3 (9.1)
>15	7 (21.2)
Years of practice
0–5 years	5 (15.2)
5–10 years	8 (24.2)
10–20 years	13 (39.4)
>20 years	7 (21.1)

ObM: Obstetric Medicine; MFM: Maternal Fetal Medicine; HDP: hypertensive disorders of pregnancy.

Reported methods used for BP determination in pregnant patients are shown in Table 2. The most frequently used method to determine pregnant women’s baseline BP was in-office (63.6%), followed by home BP (36.4%). None of the participants surveyed used 24-hour ABPM as the primary method to measure BP. The most common method for obtaining office BP measurement was auscultation (76.7%), followed by oscillometric/electronic (13.3%) and automated office BP (AOBP) monitor (10%).

Table 2.

Preferred methods of measuring blood pressure during pregnancy.

	N (%)
Obtaining baseline blood pressure (N=33)
Office	21 (63.6)
Home	12 (36.4)
24-hour ABPM	0 (0.0)
Ongoing monitoring and managing of blood pressure during pregnancy (N=32)
Office	13 (40.6)
Home	19 (59.4)
24-hour ABPM	0 (0.0)
Preferred method of measuring office blood pressure (N=30)
Auscultation	23 (76.7)
Electronic	4 (13.3)
Automated office blood pressure measurement	3 (10.0)

ABPM: ambulatory blood pressure monitor.

In contrast, home BP monitoring was the preferred method (59.4%) for ongoing monitoring and management of hypertension during pregnancy. Office BP was preferred by 40.6% of participants and no physicians surveyed used 24-hour ABPM as the primary modality for ongoing BP monitoring during pregnancy.

ObM and MFM physicians surveyed sometimes (30.3%) and usually (69.7%) attempted to differentiate WCH from true hypertension in pregnancy. Diagnosing WCH (89.5%), confirming the diagnosis of hypertension (78.9%), and improving patient education and ability for self-monitoring (73.7%) were the most common reasons physicians recommended the use of out-of-office BP measurements. More respondents did not recommend 24-hour ABPM compared to home BP monitoring, due to limited availability and costs (71.9%), long turnaround time (53.1%), unclear of validity and accuracy (34.4%) and perceived limited clinical value (12.5%) (Table 3).

Table 3.

Reasons for using or not using out-of-office blood pressure measurement for pregnant women.

	Frequency of responses (%)
Reasons for using out-of-office BP measurements (N=19)
To aid in the diagnosis of white coat hypertension	17 (89.5)
To aid in the diagnosis of hypertension	15 (78.9)
To improve patient education and ability for  self-monitoring	14 (73.7)
To detect labile blood pressure	10 (52.6)
To detect masked hypertension	7 (36.8)
Easily available tool with low or no cost	7 (36.8)
Reasons for not using home BP measurements (N=3)
Limited clinical value	3 (100)
Patient inconvenience and costs	1 (33.3)
Reasons for not using 24-hour ABPM
Limited availability and costs	23 (71.9)
Long turnaround time	17 (53.1)
Not sure of validity and accuracy	11 (34.4)
Patient preference	5 (15.6)
Limited clinical value	4 (12.5)

BP: blood pressure; ABPM: ambulatory blood pressure monitor.

The physicians surveyed provided verbal instructions on how to measure BP at home (83.3%), recommended a home BP monitor brand (23.3%), provided written instructions on how to select a home BP monitor and how to measure and record home BP readings (20.0%) or provided a home BP cuff for patients (16.7%). Only 40% of ObM and MFM specialists recommended validated home BP monitor devices to their patients as per Hypertension Canada guidelines. The most common resources physicians used to guide home BP monitoring were SOGC Hypertensive Disorders of Pregnancy 2014 guidelines (93.5%) and Hypertension Canada guidelines (25.8%).

Only 22.6% of the participants felt it was important to use BP devices validated for pregnancy. Interestingly, 64.5% of the participants preferred pregnancy-validated BP devices, but considered BP devices validated in non-pregnant women to be acceptable. The majority of clinicians surveyed (87.1%) were happy with how they were measuring BP in pregnancy. Lack of standardized procedures to measure BP, lack of validated BP devices for pregnant women and lack of appropriate sized BP cuffs were the most common barriers to accurate BP measurement in pregnant women.

Based on open-ended questions, there were varied responses for how physicians recommended the use of home BP measurements (Table 4). Some physicians recommended that patients measure their BP at home anywhere from three times per week to up to twice daily for one week. Few physicians commented on home BP targets. Of those who responded (N = 2), home BP targets recommended varied from less than 130/80 mmHg to upwards of 135–145/85–95 mmHg.

Table 4.

How clinicians recommend the use of home blood pressure measurements.

	Frequency of responses
Perceived clinical utility of home BP measurements
Rely on home BP readings over office BP  measurements	10
Provide more frequent BP readings	8
Provide patients with targets to change  medications or to present for  re-assessment	5
Assess BP trends during the day	2
Rely on home and clinic BP readings equally	2
Frequency of home BP measurement recommendations (N=6)
Twice daily for 1 week	3
Few readings per day	1
1–2 readings per day or multiple readings  overs 2 days	1
Three times per week	1
Home BP targets suggested by physicians (N=2)
135–145/85–95	1
<130/80	1

BP: blood pressure.

Discussion

ObM and MFM specialists overwhelmingly use in-office BP measurement (via auscultation) as the preferred method to diagnose hypertension, but out-of-office BP measurements, specifically home BP monitoring, were preferred for the monitoring and management of hypertension in pregnancy.

The preferred method of in-office BP measurement by auscultation for the diagnosis of hypertension does not align with the current Hypertension Canada recommendations for non-pregnant population, where unattended AOBP and out-of-office BP are preferred.² AOBP is predictive of end organ damage,¹¹ including carotid intima-medial thickness,¹² left ventricular mass,¹³ microalbuminuria¹⁴ and cardiovascular events.¹⁵ Although AOBP can approximate mean awake ambulatory BP levels, this is not a consistent finding.¹⁶ While 10% of our respondents reported on the use of unattended AOBP in pregnant women, the validity of this method is currently uncertain as no AOBP device has been validated in pregnant women.

Similar to non-pregnant population, out-of-office BP measurements was deemed important to detect WCH. WCH occurs in 30% of pregnancies,¹⁷ where BP is higher in the office than at home, and is associated with a higher risk of developing gestational hypertension, preeclampsia and caesarean delivery when compared to those without WCH.^17,18 Historically the primary modality for assessing for WCH is 24-hour ABPM; however, the definition of normal 24-hour mean and daytime BP have varied amongst studies.^17,18 Therefore, it is unclear if 24-hour ABPM thresholds used to diagnose WCH in non-pregnant population are applicable to pregnant women.

In our study, for several reasons previously listed, the majority of Canadian ObM and MFM specialists do not use 24-hour ABPM; instead, home BP monitoring was recommended. Although, ObM and MFM specialists prefer using home BP for out-of-office BP measurement, there were varied responses on how to recommend home BP measurements and home BP targets. This is consistent with the literature, where limited studies exist examining home or self-monitoring of BP in pregnant women.^18–20 Although recent individual patient data meta-analysis showed no differences between home and clinic BP measurements, the majority of the studies did not use a validated home BP monitor.²¹ There is a lack of information regarding home BP thresholds, targets, and frequency of measurements to guide clinicians for the diagnosis and management of hypertension in pregnancy as compared to the general non-pregnant population.²² When home and office BP monitoring provide discordant values, clinicians are left with uncertainty regarding targets for therapy. Moreover, there are no outcome studies evaluating the use of out-of-office BP measurements compared with in-office BP measurements during pregnancy.

Our study has a number of limitations. Given the response rate was only 48%, non-responders may have a different pattern of practice than our study population. We had missing data for the open-ended questions, and therefore the responses documented may be different than those who did not respond. Since we distributed our survey to ObM and MFM in academic, tertiary centers in Canada, the responses may not be representative of primary obstetric care providers including midwives, family doctors, general obstetricians, or those who practice in rural and community hospitals. Furthermore, costs and availability of 24-hour ABPM in different provinces may influence the utility of 24-hour ABPM throughout Canada.

Despite these limitations, our survey results are similar to those in a study conducted amongst obstetricians and family practice physicians who practice obstetrics in Alberta, Canada, which noted that 74% and 70% used home BP monitoring to identify hypertension in their pregnant women, respectively.²³ 24-hour ABPM was only recommended by 12% of obstetricians and 26% of family physicians to identify hypertension. Interestingly, frequent office BP monitoring was preferred over self-monitoring for ongoing hypertension surveillance by both obstetricians and family practice physicians. Compared with our results, a higher proportion of physicians used 24-hour ABPM, which may reflect differences in availability and costs of 24-hour ABPM in Alberta with respect to the rest of Canada.

Our study is the first Canadian study to examine the practice patterns of ObM and MFM specialists on how BP is measured in the office and out-of-office in a high-risk pregnancy cohort. These groups play a collaborative and consultative role in hypertension and preeclampsia management. We were able to recruit physicians across most regions in Canada with a diverse range of clinical experience. Furthermore, the clinicians who participated worked at high volume maternity care centers and saw a high volume of patients with hypertension in pregnancy.

Our study highlights the uncertainty in defining hypertension in pregnancy as compared to the general population. With the awareness that many of these women may actually also have WCH, out-of-office BP measurement becomes even more important.

Home BP monitoring has the advantage of more frequent BP measurements, reduced hospital visits,¹⁹ cost effective,²⁴ and patient satisfaction.²⁵ Even with the reported use of out-of-office BP measurement in pregnant women, important questions such as (a) timing, (b) frequency of home BP monitoring, (c) home BP thresholds, (d) validated home BP devices and cuff size, and (e) prediction of clinical outcomes remain unknown. Further studies are necessary to validate the use of home BP monitoring to manage hypertension in pregnancy, as well as to see if it can improve BP control and reduce maternal and neonatal morbidity.

Conclusions

Differences exist between how physicians measure BP in pregnant women and the general population. Although a greater emphasis is placed on in-office-BP measurements in pregnant women, more physicians are using home BP measurements due to recognition of WCH despite limited evidence on its use to manage hypertension in pregnancy.

Contributorship

All authors contributed to the development of the study design, survey questions, and recruitment of participants for the survey. KT was responsible for data analysis, and all authors contributed to the interpretation of the results. KT took the lead in writing the manuscript. All authors provided critical feedback and helped shape the research, analysis and manuscript.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Ethical approval

This study was approved by the University of British Columbia Research Ethics Board.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Guarantor

KT.