Clinical Practice Guidelines Antenatal care - Module I

7.3 Blood pressure

Page last updated: 02 April 2013

Measuring blood pressure in the first trimester aims to identify women with chronic hypertension (high blood pressure), which may be related to existing kidney disease. Women with hypertension are at increased risk of pre-eclampsia and require additional monitoring for other relevant risk factors.

7.3.1 Background

Healthy pregnancy is characterised by a fall in blood pressure, detectable in the first trimester, usually reaching its lowest point in the second trimester and rising to pre-conception levels towards the end of the third trimester (Lowe et al 2008). Hypertensive disorders during pregnancy include (Lowe et al 2008):
  • chronic hypertension — blood pressure ≥140 mmHg systolic and/or ≥90 mm diastolic confirmed before pregnancy or before 20 completed weeks pregnancy, without a known cause (essential hypertension), associated with a secondary cause such as existing kidney disease (secondary hypertension) or associated with measurement in a healthcare setting (white coat hypertension);
  • gestational hypertension — new onset hypertension (defined as a blood pressure ≥140 mmHg systolic and/or ≥90 mm diastolic) after 20 weeks pregnancy without any maternal or fetal features of preeclampsia, followed by return of blood pressure to normal within 3 months after the birth;
  • pre-eclampsia — a multi-system disorder characterised by hypertension and involvement of one or more other organ systems and/or the fetus, with raised blood pressure after 20 weeks pregnancy commonly the first manifestation and proteinuria a common additional feature (although not required to make a clinical diagnosis); and
  • superimposed pre-eclampsia — development of one or more of the systemic features of pre-eclampsia after 20 weeks pregnancy in a woman with chronic hypertension.

Prevalence of high blood pressure

  • The AusDiab 2005 reported an incidence of hypertension of 0.6% per year for women aged 25–34 years and 1.2% for women aged 35–44 years (Barr et al 2006). In the 2004-05 National Aboriginal and Torres Strait Islander Health Survey, high blood pressure was the most commonly reported heart and circulatory condition, affecting 5% of adults aged 25–34 years (ABS 2006).
  • Around 1–2% of women experience chronic hypertension during pregnancy (Murray et al 2002; Brown 2003) and 2–3% experience pre-eclampsia (Brown 2003). Superimposed pre-eclampsia in the second half of pregnancy occurs in about 20% of women with chronic hypertension (Lowe et al 2008).

Risks associated with high blood pressure during pregnancy

Women with chronic hypertension are at greater risk of pregnancy complications, such as placental abruption, superimposed pre-eclampsia, fetal loss, preterm labour, low birth weight, perinatal death (Jain 1997; Silbai 2002) and gestational diabetes (Hedderson & Ferrara 2008).

Risk factors for pre-eclampsia

Risk factors for pre-eclampsia include a personal or family history of pre-eclampsia, pre-existing diabetes or kidney disease, maternal hyperglycaemia (HAPO 2008), first or multiple pregnancy, raised BMI, age >40 years, more than 10 years since the last pregnancy, and raised blood pressure at the first antenatal visit (Duckitt & Harrington 2005).

7.3.2 Measuring blood pressure

Summary of the evidence

Routine measurement of women’s blood pressure at the first antenatal visit and throughout pregnancy is recommended in the United Kingdom (NICE 2008; 2010) and Canada (SOGC 2008). This advice reflects the importance of predicting the risk of pre-eclampsia to allow monitoring and preventive treatment. After 20 weeks, high blood pressure and/or proteinuria may indicate pre-eclampsia.
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Studies investigating the accuracy of blood pressure measurement and other screening tests in predicting pre-eclampsia report conflicting results. Recent studies include:
  • a systematic review (n=60,599)(Cnossen et al 2008), which found that, while mean arterial pressure is a better predictor of pre-eclampsia than systolic or diastolic blood pressure or an increase of blood pressure in the first or second trimester, its use is not supported as the sole diagnostic tool;
  • prospective studies, which also suggest the use of a combination of factors — for example maternal history, uterine artery Doppler imaging, blood pressure at 11–13 weeks, body mass index — to predict pre-eclampsia (Onwudiwe et al 2008; Poon et al 2008; 2009; Nijdam et al 2010);
  • retrospective cohort studies into screening tests, which found associations between pre-eclampsia and: maternal history of chronic hypertension, body mass index, and blood pressure; activated partial thromboplastin time (APTT), prothrombin time (PT), activated factor VIII, homocysteine, free protein S and vitamin B1; and relative plasma volume (Emonts et al 2008) and average mean arterial pressure in the first trimester (Miller et al 2007); and
  • a systematic review of screening tests (n=211,369) (Conde-Agudelo et al 2004), which found that, in women at low risk of pre-eclampsia, tests of anticardiolipin antibodies, bilateral diastolic notches during Doppler ultrasonography and urinary kallikrein had limited use and other ultrasonography characteristics and the measurement of fetal and placental peptides had low predictive accuracy and that, in women at high risk, the use of Doppler ultrasonography had low predictive accuracy and the evidence on other tests was too limited for conclusions to be drawn.
Overall there was great heterogeneity between individual studies with regard to population, gestation, definitions of pre-eclampsia, method of performing tests, test thresholds, frequency of testing, intervals between the test and outcome, and reference standards.

Recommendation Grade - B

5. Measure blood pressure at a woman’s first antenatal visit to identify existing high blood pressure.

Measuring blood pressure

Blood pressure should be measured as outlined below (NICE 2008):
  • using the woman’s right arm (Lowe et al 2008), remove tight clothing and ensure arm is relaxed and supported at heart level;
  • use cuff of appropriate size (eg use a large cuff if arm circumference is >33cm and a thigh cuff if it is >42cm);
  • inflate cuff to 20–30 mmHg above palpated systolic blood pressure;
  • lower column slowly, by 2 mmHg per second or per beat;
  • read blood pressure to the nearest 2 mmHg; and
  • measure diastolic blood pressure as disappearance of sounds (phase V; or IV if phase V is absent).
Women with a single diastolic blood pressure reading of 110 mmHg or more, or two consecutive readings of 90 mmHg or more at least 4 hours apart and/or significant proteinuria (1+) require increased monitoring and treatment should be considered. Women with a systolic blood pressure equal to or above 140 mmHg on two consecutive readings at least 4 hours apart require further assessment and treatment should be considered.

Automated blood pressure measuring devices

Although mercury sphygmomanometry remains the gold standard for measuring blood pressure, due to environmental and safety concerns its use is declining and automated devices are increasingly being used in the general hypertensive population (Brown et al 2011). Few studies have compared these devices with sphygmomanometry in pregnant women (Lowe et al 2008). While they may give similar mean blood pressure values to those obtained with sphygmomanometry, there is wide intra-individual error and their accuracy may be further compromised in pre-eclamptic women (Gupta et al 1997; Brown et al 1998).

The potential errors of automated devices may be offset by comparing blood pressure recordings by routine mercury sphygmomanometry (Brown et al 2011). Considerations with automated devices include:
  • using only devices that have been validated for use in pregnancy by the British Hypertensive Society, the Association for the Advancement of Medical Instruments or other accepted and published criteria;
  • maintaining some mercury sphygmomanometers for the purpose of allowing regular calibration of all devices; and
  • when a pregnant woman uses an automated device for home blood pressure measurements, checking the device against mercury sphygmomanometry to ensure accuracy of readings.

White coat hypertension

White coat or “office” hypertension occurs in early pregnancy with the same frequency as it does in non-pregnant women (Brown et al 2005). A prospective study (n=241) (Brown et al 2005) found that 32% of women early in pregnancy who were given an initial diagnosis of essential hypertension had white coat hypertension. Half of these women retained this phenomenon throughout pregnancy and had good pregnancy outcomes, 40% developed (benign) gestational hypertension and also had good pregnancy outcomes and 8% developed proteinuric pre-eclampsia, which was significantly fewer than in women with confirmed essential hypertension (22%).
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Women with pre-existing hypertension

Women presenting for antenatal care currently on medication for hypertension should have their medicines reviewed to ensure their safety in pregnancy.
Considerations beyond the first trimester
  • Any woman presenting with new hypertension after 20 weeks pregnancy should be assessed for signs and symptoms of pre-eclampsia.
  • The presence of hypertension and/or proteinuria should alert the healthcare professional to the need for increased surveillance (NICE 2008).

7.3.3 Practice summary — measuring blood pressure

When — At first antenatal visit
Who — Midwife; GP; obstetrician; Aboriginal and Torres Strait Islander health worker; multicultural health worker
  • Explain the risks associated with high blood pressure in pregnancy — Discuss the importance of identifying high blood pressure early in pregnancy.
  • Offer lifestyle advice — Highlight to women who experience raised blood pressure in pregnancy the benefits of not smoking, maintaining a healthy weight, regular physical activity and a healthy diet.
  • Arrange treatment or referral if required — For women with chronic hypertension, further testing may be required to exclude white coat hypertension or kidney disease and treatment may be needed.

7.3.4 Resources

British Hypertensive Society Automatic Digital Blood Pressure Devices for Clinical Use. www.bhsoc.org/bp_monitors/automatic_clinic.stm (This website link was valid at the time of submission)
Lowe SA, Brown MA, Dekker G et al (2008) Guidelines for the management of hypertensive disorders of pregnancy 2008. Society of Obstetric Medicine of Australia and New Zealand. Aust NZ J Obstet Gynaecol 49(3): 242–46. For more information please visit SOMANZ website.
NICE (2010) Hypertension in Pregnancy: the Management of Hypertensive Disorders during Pregnancy. National Collaborating Centre for Women’s and Children’s Health. Commissioned by the National Institute for Health and Clinical Excellence. London: RCOG Press.
SOGC (2008) Diagnosis, Evaluation, and Management of the Hypertensive Disorders of Pregnancy. Clinical Practice Guideline No. 206. Toronto: Society of Obstetricians and Gynaecologists of Canada.

7.3.5 References

ABS (2006) National Aboriginal and Torres Strait Islander Health Survey 2004–2005. ABS Cat No 4715.0. Canberra: Australian Bureau of Statistics.

Barr ELM, Magliano DJ, Zimmet PJ et al (2006) AusDiab 2005 The Australian Diabetes, Obesity and Lifestyle Study. Tracking the Accelerating Epidemic: Its Causes and Outcomes. Melbourne: International Diabetes Institute.

Brown MA (2003) Pre-eclampsia: a lifelong disorder. Med J Aust 179 (4): 182–84.

Brown MA, Mangos G, Davis G et al (2005) The natural history of white coat hypertension during pregnancy. Brit J Obstet Gynaecol 112(5): 601–06.

Brown MA, Robinson A, Buddle ML (1998) Accuracy of automated blood pressure recorders in pregnancy. Aust NZ J Obstet Gynaecol 38: 262–65.

Brown MA, Roberts LM, Mackenzie C et al (2011) A prospective randomized study of automated versus mercury blood pressure recordings in hypertensive pregnancy (PRAM Study). Hypertens Pregnancy iFirst: 1–13.

Cnossen JS, Vollebregt KC, de Vrieze N et al (2008) Accuracy of mean arterial pressure and blood pressure measurements in predicting preeclampsia: systematic review and meta-analysis. Brit Med J 336(7653): 1117–20.

Conde-Agudelo A, Villar J, Lindheimer M (2004) World Health Organization systematic review of screening tests for preeclampsia. Obstet Gynecol 104: 1367–91.

Duckitt K & Harrington D (2005) Risk factors for pre-eclampsia at antenatal booking: systematic review of controlled studies. Brit Med J 330(7491): 565.

Emonts P, Seaksan S, Seidel L et al (2008) Prediction of Maternal Predisposition to Preeclampsia. Hypertens Preg 27: 237–45.

Gupta M, Shennan AH, Halligan A et al (1997) Accuracy of oscillometric blood pressure monitoring in pregnancy and pre-eclampsia. Brit J Obstet Gynaecol 104: 350–55.
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HAPO (2008) Hyperglycemia and adverse pregnancy outcomes. HAPO Study Cooperative Research Group. N Engl J Med 358: 1991–02.

Hedderson MM & Ferrara A (2008) High blood pressure before and during early pregnancy is associated with an increased risk of gestational diabetes mellitus. Diabetes Care 12: 2362–67.

Jain L (1997) Effect of pregnancy-induced and chronic hypertension on pregnancy outcome. J Perinatol 17: 425–27.

Lowe SA, Brown MA, Dekker G et al (2008) Guidelines for the management of hypertensive disorders of pregnancy 2008. Society of Obstetric Medicine of Australia and New Zealand. Aust NZ J Obstet Gynaecol 49(3): 242–46.

Miller RS, Rudra CB, Williams MA (2007) First-Trimester Mean Arterial Pressure and Risk of Preeclampsia. Am J Hypertens 20(5): 573–78.

Murray N, Homer CS, Davis GK et al (2002) The clinical utility of routine urinalysis in pregnancy: a prospective study. Med J Aust 177: 477–80.

NICE (2008) Antenatal Care. Routine Care for the Healthy Pregnant Woman. National Collaborating Centre for Women’s and Children’s Health. Commissioned by the National Institute for Health and Clinical Excellence. London: RCOG Press.

NICE (2010) Hypertension in Pregnancy: the Management of Hypertensive Disorders during Pregnancy. National Collaborating Centre for Women’s and Children’s Health. Commissioned by the National Institute for Health and Clinical Excellence. London: RCOG Press.

Nijdam ME, Janssen KJM, Moons KGM et al (2010) Prediction model for hypertension in pregnancy in nulliparous women using information obtained at the first antenatal visit. J Hypertens 28(1): 119–26.

Onwudiwe N, Yu CK, Poon LC et al (2008) Prediction of preeclampsia by a combination of maternal history, uterine artery Doppler and mean arterial pressure. Ultrasound Obstet Gynecol 32(7): 877–83.

Poon LC, Kametas NA, Pandeva I et al (2008) Mean arterial pressure at 11(+0) to 13(+6) weeks in the prediction of preeclampsia. Hypertension 51(4): 1027–33.

Poon LCY, Karagiannis G, Leal A et al (2009) Hypertensive disorders in pregnancy: Screening by uterine artery Doppler imaging and blood pressure at 11–13 weeks. Ultrasound Obstet Gynecol 5: 497–502.

Sibai B (2002) Chronic hypertension in pregnancy. Am J Obstet Gynecol 100: 369–72.

SOGC (2008) Diagnosis, Evaluation, and Management of the Hypertensive Disorders of Pregnancy. Clinical Practice Guideline No. 206. Toronto: Society of Obstetricians and Gynaecologists of Canada.