Cardiovascular Journal of Africa: Vol 30 No 2 (March/April 2019)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 2, March/April 2019

AFRICA

121

In 2018, the International Society for the Study of

Hypertension in Pregnancy (ISSHP) classified HDP as PE,

transient gestational hypertension, gestational hypertension,

white-coat hypertension, masked hypertension, chronic

hypertension and chronic hypertension with superimposed

PE.

PE is the development of new-onset hypertension in

pregnancy at or beyond the gestational age of 20 weeks, with

the presence of significant proteinuria and/or maternal organ

dysfunction or placental insufficiency.

Gestational hypertension

is a new-onset hypertension after 20 weeks of gestational age.

Transient gestational hypertension is transient occurrence of

hypertension at any stage of pregnancy with spontaneous

resolution without treatment. Chronic hypertension is that which

exists prior to 20 weeks’ gestational age. White-coat hypertension

is the occurrence of hypertension only in a medical practitioner’s

office/clinic with normalisation of the blood pressure (

135/85

mmHg) outside the health facility.

1, 32

Masked hypertension is

the occurrence of hypertension in other settings other than the

medical practitioner’s office/clinic setting.

Gestational hypertension (15–25%)

and chronic hypertension

(25%)

will progress to PE. Additionally, 20% of patients with

transient gestational hypertension will develop either gestational

hypertension or PE.

Data on white-coat hypertension and

masked hypertension in pregnancy are limited, but these

disorders are not innocuous. For instance, 40 and 8% of white-

coat hypertension will progress to gestational hypertension and

PE, respectively.

Haemodynamic and vascular changes that

affect accuracy of blood pressure measurement

Haemodynamic and cardiovascular changes occur in pregnancy,

resulting in hyperdynamic circulation,

with aberrations in this

physiology contributing to clinical features of HDP. Of note,

blood pressure is the product of cardiac output and systemic

vascular resistance, and blood pressure monitors function by

assessing the blood flow and or changes in the vessel wall.

In pregnancy, stroke volume and heart rate are increased and

these elevate the cardiac output, and in tandem, the peripheral

vascular resistance is decreased.

Pregnancy also increases the

production of relaxin, which remodels or softens collagen by

degradation via upregulation of both matrix metalloproteinases

and tissue inhibitors of metalloproteinases.

In the non-pregnant

state, relaxin has also been found to reverse fibrosis, possibly

by preventing collagen synthesis through downregulation of

fibroblast activation, proliferation and secretion.

These changes

occur in the vasculature, alter the stiffness/compliance and

capacitance of the vessel wall, and these mechanisms are

acceptable to investigators.

39-43

In fact, it has been reported that

the arterial compliance is increased by 30% in the first trimester

and remains elevated thereafter during pregnancy.

In PE, mediators such as soluble fms-like tyrosine kinase-1

(sFlt-1) injure the endothelium and alter vascular reactivity.

44,45

Therefore, vascular compliance in non-pregnancy, healthy

pregnancy

and HDP

differs, and blood pressure devices

require validation in these conditions. The changes in vascular

compliance support the use of augmentation index and pulse-

wave velocities (both of which are measures of arterial stiffness)

as indices of cardiovascular risk in early pregnancy

and after a

pre-eclamptic pregnancy.

Importance of accurate blood pressure meas-

urement in pregnancy

Accurate measurement of blood pressure assesses the overall

health status and is crucial in the antenatal, intrapartum

and postpartum periods and impacts on both maternal and

perinatal outcomes. In the antenatal period (but not limited

to this period), measurement of blood pressure is useful for:

(1) screening for PE: the US Preventive Services Task Force

recommends blood pressure measurement during each prenatal

visit as the method of screening for HDP;

(2) prediction of

adverse pregnancy outcomes such as foetal growth restriction

and/or PE;

51,52

(3) diagnosis of cardiovascular diseases: apart

from hypertension, measurement of blood pressure on both right

and left arms during the first clinic visit may reveal a significant

pressure difference that will assist in the diagnosis of coarctation

of the aorta; and (4) helps to trigger the commencement and

adjustment of the dose of antihypertensive medication.

The following is the usefulness of intrapartum blood

pressure measurement. (1) During labour, blood flows from the

uteroplacental vasculature

to the rest of the circulation. This

increases the stroke volume, cardiac output (11%),

and blood

pressure. Therefore, care must be taken to monitor the blood

pressure to safeguard against complications such as stroke,

eclampsia and cardiac failure. (2) The presence of hypertension

during endotracheal intubation is a risk factor for stroke during

the procedure. (3) Blood pressure measurement will also assist

in the diagnosis of hypotension and calculation of shock index

(pulse rate divided by systolic blood pressure), which may assist

in determining the need for blood transfusion in a bleeding

patient and predicting adverse pregnancy outcomes. It has

been shown that in a study involving 958 women with obstetric

haemorrhage in a low-resource setting that a shock index

0.9

indicates the need for referral while

1.4 signals the need for

urgent intervention, including blood transfusion in a tertiary

centre.

It is important to note that rate pressure product, which is

a product of systolic blood pressure (mmHg) and pulse rate,

is different from shock index. Rate pressure product indicates

cardiac oxygen consumption and may be useful in individuals

who are anaesthetised or exercising.

55,56

Future studies are

required to possibly expand its role in pregnancy and HDP.

In the postpartum period, measurement of blood pressure

is useful for the diagnosis of hypotension, which may signal

postpartum haemorrhage, or in the diagnosis of severe

hypertension, which may result in catastrophic complications

such as eclampsia and stroke. It is important to note that the

majority of cases of postpartum eclampsia occur in the first

to 72

hours following childbirth. Therefore the patient,

particularly those with a diagnosis of HDP, must have frequent

blood pressure measurements in this period. Understandably,

a lack of hospital beds may lead to early hospital discharge,

but in such circumstances out-patient or home blood pressure

monitoring is mandatory.

Blood pressure-measuring devices

Blood pressure devices may be broadly categorised into invasive

(intra-arterial line) and non-invasive. The non-invasive types

are auscultatory and non-auscultatory. Mercury, aneroid and

non-mercury liquid crystal

sphygmomanometers are examples