Raised blood pressure (BP) affects ~10% of pregnancies, and is associated with an increased risk of developing pre-eclampsia, and in the long-term an increased risk of chronic hypertension and cardiovascular disease [1, 2]. The early detection and subsequent management of pregnancy hypertension is important, in order to optimise pregnancy outcomes for the woman and infant. Unlike BP monitoring and management outside of pregnancy, BP can change rapidly during pregnancy and changes can be difficult to predict [1].

Self-monitoring of blood pressure (SMBP), where an individual measures their own BP outside of the clinical setting, is effective at detecting and lowering blood pressure in adults with hypertension, and now commonplace outside of pregnancy [3,4,5]. In pregnancy and the postnatal period, SMBP has the potential to improve the detection and management of raised BP whilst empowering women and potentially reducing clinic visits [6].

Interest in the opportunities for SMBP in pregnancy and the postnatal period is increasing. In the last five years, several studies have reported research around the use of SMBP during pregnancy, from settings around the world including Europe, Asia and North America. Early work from small observational studies suggested the potential for reduced morbidity and resource use, as well as acceptability and feasibility, yet evidence from large-scale randomised trials for the effectiveness of SMBP in pregnancy has been lacking until recently [7,8,9]. This article reviews the findings from the Blood Pressure Monitoring in Pregnancy (BUMP) programme of work, undertaken in the United Kingdom (UK), in this rapidly developing area [10,11,12,13].

Prevalence of self-monitoring of blood pressure

A large UK survey in 2019 of pregnant individuals found that overall, around one in five were currently self-monitoring their BP; of those who self-identified as hypertensive, half reported SMBP. However, many of those self-monitoring did not share their readings with their antenatal care team and were not necessarily using pregnancy-validated BP monitors [12]. These findings are in line with a Canadian-based study, which found more than 60% of pregnant women diagnosed with hypertension were already undertaking SMBP [14]. This evidence suggests SMBP has become relatively widespread, and so health care professionals (HCPs) should enquire about SMBP proactively and consider providing information on BP monitoring.

Self-monitoring thresholds in pregnancy are not clear

A systematic review and individual patient data analysis aimed to explore BP thresholds in pregnancy. The search found over 20 studies and analysed patient data from eight studies (n = 758), revealing a mean home-clinic difference of just ≤1.2 mmHg systolic BP throughout pregnancy. However, there was significant heterogeneity between studies (I2 > 80%); only one study was randomised, and only two of the studies used a monitor validated for use in pregnancy. Although the overall population difference was small (around 2 mmHg systolic), levels of ‘white coat hypertension’ were high, particularly towards the end of pregnancy, when around half of those with clinic hypertension had normal range home readings. The home-office difference was much greater in those with hypertension (predominantly over 10 mmHg systolic through pregnancy) [15]. Data from the OPTIMUM pilot trial and BUMP trials show similar findings [16, 17]. More recent systematic reviews (not including the BUMP trial data) report similar findings with significant clinical heterogeneity [9].

Trials of self-monitoring of blood pressure

Until recently, few data were available regarding SMBP as an intervention in pregnancy; a systematic review found just one previous randomised controlled trial of self-monitoring in an antenatal setting with normotensive women [18]. This included 80 low-risk pregnancy women who were randomised to undertake either weekly self-monitoring with reduced routine antenatal clinics or usual care (but did not evaluate the impact of self-monitoring on the timing of new diagnoses of pregnancy hypertension). We found one additional trial in which a US group randomised 300 low-risk pregnant women to remote monitoring with reduced clinic visits or usual care. The women randomised to remote care had reduced obstetric input but more nurse/midwife time was needed for the remote care. Other maternal and perinatal outcomes were similar between the groups. The BUMP pilot study and OPTIMUM-BP pilot trial established feasibility in the UK health service of SMBP in higher risk and hypertensive pregnancies and supported the development of the BUMP trials, which aimed to assess the place of self-monitoring in the diagnosis (BUMP1) and management (BUMP2) of hypertension in pregnancy [10, 11].

The BUMP trials were two fully powered randomised controlled trials of SMBP in pregnancy that recruited more than 3000 women at higher risk of pre-eclampsia, or with pregnancy hypertension. Participating women were randomly allocated to either usual care or usual care plus SMBP.

The BUMP1 trial recruited 2441 pregnant women at higher risk of pre-eclampsia around 20 weeks’ gestation with the aim of detecting raised BP earlier than standard clinic visits. The trial found that SMBP during higher-risk pregnancy appeared to be safe, but did not significantly improve earlier clinic-based detection of hypertension when used alongside usual care. Despite this, there was a signal of the potential of SMBP: self-monitoring did provide potential prior notice of hypertension in many women, with 61% (109/179) of those with hypertension reporting raised SMBP around one month prior to clinic diagnosis (median 29 days earlier). This suggests that SMBP in pregnancy could have been used to detect hypertension earlier, but the information was not necessarily acted upon by clinicians (or possibly by women). Further work is required to assess the place of self-monitoring of BP in this higher-risk population, for instance in remote consultations or alongside self-management, and to understand how to better engage HCPs in its use [11].

The BUMP2 trial recruited 850 women with gestational or chronic hypertension, with the aim of improving BP control (as had been found outside of pregnancy) [4]. The intervention of SMBP did not result in improved BP control as assessed by clinic systolic BP but was acceptable, with no difference in adverse maternal or infant outcomes, and was equivalent in cost to usual care alone [19]. As with using monitoring for earlier diagnosis, further co-interventions may be required in order to achieve improvements in BP control and other pregnancy outcomes [10].

For the BUMP2 trial, many women’s average blood pressure was above the NICE target of 135/85mmHgh based on their clinic readings, suggesting additional titration of antihypertensive medication might have been needed [10]. Additionally, a higher proportion than expected in the usual care arm (68%) reported prior SMBP, but these data were not available during the trial itself. These considerations, in combination with the survey results, suggest that SMBP is already part of women’s health behaviours but has not yet been fully or formally incorporated into care pathways [12].

Understanding the trial findings

A process evaluation of the trials showed that the majority of women and healthcare professionals involved in the trial found that SMBP enhanced their experiences of the clinical encounter and the HCP-woman relationship [20, 21]. However, the pursuit of normal readings, selective or delayed reporting of raised readings, and variable engagement by HCPs with home readings, could have influenced the impact of the BUMP intervention. Interviews and observations suggest that SMBP led to both earlier detection of rising BP, but also was used as justification for not starting intensifying antihypertensive medication when home readings were lower [20, 21]. Finally, SMBP by women in the usual care arm may have reduced between-groups differences, limiting the evidence for the intervention’s effectiveness.

What helps (or hinders) SMBP in practice?

Qualitative work from linked studies showed that women were highly motivated and empowered by SMBP, reporting greater control, knowledge and reassurance. Interviews and ethnographic observations showed that good communication and effective partnerships between women and clinicians underpinned the use of SMBP, and may in turn have supported shared decision-making [22].

However, uncertainty remains around home-clinic differences and how this information could be translated into clinical decisions, with the qualitative work in the BUMP trials revealing that some clinicians had higher confidence in clinical readings (rather than home readings) when it came to taking action [15, 20].

Proteinuria self-testing in pregnancy

Linked to the BUMP programme, the Proteinuria Detection In Pregnancy (UDIP) diagnostic accuracy study compared the performance of proteinuria testing by women, midwives and automated colorimetric readers. It showed that pregnant women could detect dipstick proteinuria with similar accuracy to healthcare professionals, suggesting urine self-testing alongside BP self-monitoring would be feasible. Furthermore, the study also showed that automated colorimetric testing was not significantly different to performance by women or healthcare professionals. Although the accuracy of urine dipstick testing is not as high as desired in a diagnostic test, testing in the context of antenatal care, which includes repeated testing, is likely to be beneficial [13]. Furthermore, using protein testing in combination with home BP monitoring could allow better reassurance to both healthcare professionals and women that the important indicators of evolving pre-eclampsia are being monitored.

The cost-effectiveness of SMBP

Cost-effectiveness analyses of the BUMP 1&2 trials showed that SMBP had no additional cost over and above usual care [19]. The use of SMBP may be better value for money when used for women with pregnancy hypertension than for women at risk of hypertension, due to a greater risk of developing complications both during and following pregnancy in these women. These findings are in keeping with previous smaller cost-effectiveness studies in the Netherlands and the UK [23, 24]. A key issue is provision of validated monitors and in the future they might also be available for post-partum monitoring and beyond as this is often warranted [25,26,27]. During the COVID-19 pandemic, the National Health Service in England provided some BP monitors for those with hypertensive pregnancy (see below) and some hospitals may have a small number of monitors for loan [28]. However, for many in the UK, the only option for a pregnant woman is to purchase a monitor, which may result in exclusion of some groups.

Acceptability of SMBP in the BUMP trials

The SMBP studies described above had good uptake, and linked qualitative work has shown that SMBP is acceptable to higher risk and hypertensive pregnant women and their antenatal care teams [7]. A recent survey suggests that most UK obstetricians (96%) now consider SMBP to be part of current antenatal care [29]. While SMBP during pregnancy has been shown to be acceptable, safe, and no more expensive than usual care, the challenge now is to understand how it can be most effectively integrated into existing care pathways and used to make improvements to outcomes.

Could self-monitoring be used to guide tighter BP control?

The CHIPS international study of targeting diastolic BP as the intervention showed that tighter control of hypertension was associated with fewer severe hypertension episodes and is safe [30]. More recently, the CHAP study has shown that antihypertensive treatment of mild to moderate chronic hypertension improves pregnancy outcomes, without increased detection of babies small for gestational age [31]. There is a clear rationale for managing women’s blood pressure with tight control, targeting a diastolic BP of 85 mmHg. SMBP could support this change in practice towards earlier and more active management, but would require further work in ensuring that women and healthcare professionals understand and take appropriate action on self-monitored BP readings.

Lessons from rapid implementation of SMBP during the COVID-19 pandemic

The COVID-19 pandemic resulted in an urgent shift from clinic-based maternity care to greater remote monitoring, necessitating the rapid implementation of SMBP. In the UK, guidelines were quickly produced, recommending that SMBP was prioritised for women with hypertension or pre-eclampsia, those with risk factors, or those required to self-isolate [32]. Implementation was further supported by the provision of BP monitors by the National Health Service in England, validated for use in pregnancy. During this time, SMBP was predominantly used to provide additional BP monitoring for hypertensive or high-risk pregnant women, rather than replacing face-to-face visits for normal-risk women. Maternity units and women were positive about monitoring to reduce clinic visits and to give women more control and insight into their own BP. However, there were implementation challenges particularly around embedding SMBP into existing care pathways, interpreting readings and managing the provision of monitors [28]. This revealed a need for further research into appropriate care pathways and information and guidance around management of white coat or masked (high home BP readings, normal clinic readings) hypertension.

These implementation studies are part of a wider emerging evidence base and health system interest in virtual care [33]. The rapid reconfiguration of antenatal services in response to the pandemic has highlighted a significant shift to remote provision, of which SMBP was an integral component [34,35,36]. A large UK study undertaken during the COVID-19 pandemic, highlighted the potential accessibility and efficiency advantages of remote antenatal care reported by women including saving time, stress, travel expenses and reducing time off work and/or childcare [7]. The study enabled the development of a maternity-specific framework of the domains of quality that appear most relevant to stakeholders in remote antenatal care: efficiency and timeliness; effectiveness; safety; accessibility; equity and inclusion; person-centredness and choice and continuity [37].