Hypertension is a significant problem, both in the general population and among pregnant women, with around one in 10 women experiencing a form of hypertensive disorder during pregnancy.1 It is the third most common direct cause of maternal mortality worldwide, after haemorrhage and infection,2 and is also associated with adverse affects to the baby, including intrauterine growth retardation, premature delivery and respiratory distress syndrome.3
Current guidelines state that blood pressure should be monitored routinely at antenatal appointments, with increased frequency in high-risk pregnancy and if problems develop.4 Self-monitoring enables women to monitor their own blood pressure between routine appointments, potentially identifying hypertension earlier and aiding management once it is established.5
Self-monitoring is becoming increasingly popular among patients and healthcare professionals. One US study found that 60% of women with hypertension in pregnancy were self-monitoring.6 However, few studies have assessed its safety and effectiveness and whether it will have any effect on the outcomes of pregnancy.5
Accuracy of self-monitoring
Clear thresholds for self-monitoring of hypertension during pregnancy have yet to be established,7 making assessing its utility tricky. Blood pressure fluctuates through the trimesters; with a small drop in blood pressure over the first two trimesters and a subsequent return to non-pregnant levels in the third trimester. As with hypertension in the general population, 140/90 mmHg is the accepted threshold for the diagnosis of hypertension across all trimesters.8
Despite there already being a large number of home monitors available for self-monitoring, only five have been validated and deemed accurate for use during pregnancy.5 Interestingly, some monitors validated in a general population are inaccurate in pregnant women, mostly due to clinically significant false low readings.9 The cause of this is thought to be due to reduced arterial compliance, increased systemic vascular resistance, and increased intravascular volume, which can lead to an incorrect reading at a given pressure in the cuff.10 Peripheral oedema is also present in 80% of normal pregnancies, with the majority of this occurring during the second trimester.11 This may cause blood pressure monitors to underestimate diastolic pressure by a clinically significant average of 9 mmHg.12 Obesity can also affect the ability of otherwise accurate monitors to operate in pregnancy.13 Despite this, a recent Australian study showed that many devices used opportunistically by women are accurate in pregnancy, but that up to a quarter of them will have a blood pressure difference of at least 5 mmHg compared against an accurate reference standard.14
Self-monitoring outside of pregnancy has been reported to be associated with selective reporting of blood pressure.15 However, given an accurate monitor, it appears women are able to self-monitor and report back accurately: an observational study showed that only 2.9% of home blood pressure readings were inaccurate (compared to monitor memories) among women who were at high risk of pre-eclampsia.16 These results indicate that self-monitoring is entirely feasible among high-risk groups.
Effects on pregnancy outcomes
One of the main advantages of self-monitoring is the potential for more frequent monitoring, hence, the hope that this will allow earlier detection of hypertensive disorders, such as pre-eclampsia. A study showed that 81% of women who were self-monitoring did at least six blood pressure measurements a day, and all women involved did at least two measurements per week.17 There is also potential for self-monitoring to free the time of healthcare professionals, as it could reduce the need for additional antenatal appointments simply to measure blood pressure. Another potential benefit is increased treatment compliance: outside of pregnancy, studies have shown a small but significant effect on medication adherence.18
It is not yet known whether self-monitoring will alter pregnancy outcomes due to a lack of available evidence. A pilot randomised-controlled trial compared a control group receiving nine antenatal visits to an experimental group with a reduced number of appointments but who were also self-monitoring. There was an increase in unscheduled visits in the experimental group, however, there were fewer visits overall and an increase in the overall number of blood pressure measurements taken. The majority of the women in the study stated they preferred self-monitoring and there was no significant difference in levels of anxiety experienced between the two groups.19 This shows that self-monitoring is seen as acceptable to pregnant women. A larger trial would be required to indicate whether there would be an effect on the outcomes of pregnancy, but this pilot study indicates that a larger trial should be feasible and safe.
Several new studies are currently underway, one of which is looking at whether self-monitoring of blood pressure can lead to an earlier diagnosis of raised blood pressure in pregnancy.20 Evidence from studies, such as this, should give an indication as to whether self-monitoring could be beneficial for diagnosis and management of hypertension during pregnancy.
Medicalisation of healthcare
Pregnancy and childbirth have been described as becoming increasingly medicalised since the early 20th century, and to some, self-monitoring may be seen as further medicalisation.21 The responsibility of frequent self-monitoring of blood pressure could be too much for some patients, and this could induce problems, such as anxiety, as they may find it too much pressure or commitment, especially if they have to take multiple readings per day. In addition to this, some patients may get obsessive over their blood pressure readings and check them more often than required or may overreact about small changes in their readings. This could in turn lead to increased blood pressure due to anxiety.
On the other hand, to a patient who may not have a great deal of medical knowledge, they might not understand the purpose and importance of monitoring blood pressure. Self-monitoring could help to break down barriers between the doctor and patient as it would allow for greater patient involvement in their healthcare, and the patient may feel more in control. A post-partum questionnaire showed that 98% of women with hypertension liked being involved in their blood pressure management.6 Therefore, self-monitoring could simultaneously be seen to decrease the medicalisation of pregnancy.
What happens next?
As mentioned previously, self-monitoring is becoming increasingly popular and research has suggested that pregnant women prefer this method of monitoring over clinic and ambulatory measurements.
However, there is currently a lack of evidence to suggest whether self-monitoring during pregnancy is the best way forward and whether it will have any impact on the outcomes of pregnancy. In order to establish self-monitoring as safe and effective during pregnancy, further research is needed to ensure it is the best option for both mother and baby.
Conflict of interest
JW: none declared. RJM has received blood pressure monitors for research purposes from Lloyds Pharmacy and Omron.
References
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