Diagnosis

In the authors' opinion, the cornerstone of care for women with sus­pected or confirmed pregnancy hypertension is making an accurate diagnosis of both hypertension and/or proteinuria.

The major haemodynamic changes of pregnancy include an increase in sodium and water retention leading to blood volume expansion, an increase in cardiac output, and reductions in both systemic vascular resistance and systemic blood pressure (BP). Beginning in early pregnancy, these changes reach their sustained peak during the second trimester, remaining relatively con­stant until delivery. While plasma volume expands by approxi­mately 50%, the red cell mass increases by 40%, resulting in the physiological anaemia of pregnancy. Women who are destined to develop pre-eclampsia may not have the mid-trimester fall in BP and have relative haemoconcentration.

Measurement of blood pressure

The definition of hypertension in pregnancy is a challenging task because BP levels in pregnancy are dynamic, have a circadian rhythm, and change by gestational age (16). Therefore, the diagnosis of pregnancy hypertension should be based on outpatient clinic or in-hospital BP measurements. This mirrors recommendations by general hypertension guidelines outside pregnancy, such as those of the Canadian Hypertension Education Program (17).

The accepted definition is a diastolic BP (DBP) of at least 90 mmHg and/or a sustained systolic BP (SBP) of at least 140 mmHg by re­peated measurements in the same arm until a steady BP reading is achieved (15, 17, 18), rather than the historical definition of 4 or more hours apart. There is less certainty about a diagnosis of hyper­tension based on only SBP between 140 and 159 mmHg, as opposed to DBP criteria.

Severe hypertension should be defined, in any setting, as a SBP of at least 160 mmHg or a DBP of at least 110 mmHg based on the average of at least two measurements, repeated either until steady readings are achieved or at least 15 minutes apart, using the same arm (15, 19).

Isolated office (‘white coat') hypertension is defined as an out­patient clinic SBP of at least 140 mmHg or a DBP of at least 90 mmHg, but an ambulatory BP monitoring (ABPM) or home BP monitoring (HBPM) SBP less than 135 mmHg and DBP less than 85 mmHg (15). In contrast, a normal office BP with elevated ABPM or HBPM (‘masked hypertension') should be defined as an out­patient clinic SBP less than 140 mmHg or a DBP less than 90 mmHg, but an ABPM or HBPM SBP of at least 135 mmHg or DBP of at least 85 mmHg (15).

There are several issues of consideration specific to the measure­ment of BP during pregnancy. The technique should be standard­ized, as it should be outside pregnancy. BP can be measured using validated and calibrated auscultatory (mercury or aneroid devices) or automated methods. Factors to consider when selecting a BP measurement device include validation, disease specificity, observer error, and the need for regular recalibration (20).

Validation of BP devices is a process by which the accuracy of a device is assessed, over a range of BP readings, on several occasions and for women with different HDPs. Observer error (e.g. terminal digit preference to numbers ending in ‘0’ and ‘5’) can be eliminated by automated BP measurement devices. Calibration involves com­paring readings from an aneroid or automated BP machine with those taken with a mercury manometer. Only some devices have been validated in pre-eclampsia (Dinamap ProCare 400, Microlife 3AS1-2, Microlife 3BTO-A, Nissei DS-400, Omron-MIT, and Omron-MIT Elite) (18, 21-25). Most other automated devices will tend to underestimate both SBP and DBP by 5-15 mmHg—a sys­tematic error that places women at risk.

There are three categories of BP monitoring methods: (a) office BP measurement, (b) ABPM, and (c) HBPM (15, 17). In the past two decades, both ABPM and HBPM have gained popularity in confirming diagnosis and improving BP monitoring, compliance with antihypertensive medication, and achievement of BP targets.

However determined, a diagnosis of hypertension in pregnancy in a community setting is consistent with a daytime ABPM or average HBPM of SBP of at least 135 mmHg or DBP of at least 85 mmHg (15).

As stated previously, less developed countries bear a dispropor­tionate burden of maternal morbidity and mortality from the HDP. While regular BP monitoring can cost-effectively reduce this dis­parity, less developed country health systems face unique challenges which reduce this capacity (26-39). Continued efforts to address these challenges through implementation and evaluation of inter­ventions informed by robust needs assessments is urgently needed to strengthen the capacity of health systems to provide good mater­nity care and reduce maternal and neonatal outcome disparities in less developed countries.

Measurement of proteinuria

In the authors’ opinion, all pregnant women should be assessed for proteinuria, at minimum, at their first antenatal visit, and it should repeated, if not at every antenatal visit, whenever either hypertension is detected or symptoms suggestive of pre-eclampsia are declared (14, 15). Urinary dipstick testing (or sulphosalicylic acid (SSA) or heat coagulation testing if dipsticks are not available) may be used to screen for proteinuria when the suspicion of pre-eclampsia is low, and significant proteinuria should be strongly suspected when urinary dipstick proteinuria is 2+ or greater (14, 15).

Definitive testing for proteinuria (by urinary protein:creatinine ratio or 24-hour urine collection) is encouraged when there is a suspicion of pre-eclampsia, with significant proteinuria defined as at least 0.3g∕day in a complete 24-hour urine collection or at least 30 mg/mmol (≥0.3 mg∕mg) urinary creatinine in a random urine sample. It should be remembered that 24-hour urine collections are prone to both under- and over-collection approximately half of the time, with even splitting between under- and over-collections (40). Although increasingly used outside pregnancy, currently there is insufficient information to make a recommendation about the ac­curacy of the urinary albumin:creatinine ratio, although values less than 2 mg/mmol (21.1 Classification of the hypertensive disorders of pregnancy