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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 27, No 2, March/April 2016
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AFRICA
pressure and a reduction in the requirement for treatment at
this point in the pregnancy. As the volume expansion during
pregnancy continues and peaks at about 32 weeks’ gestation, the
need for treatment may increase again. The goals of treatment
also may need to be revised during pregnancy.
Outside pregnancy, the aim of treatment is prevention of
end-organ damage to the heart, vasculature and kidneys. The
use of diuretics with ACE inhibitors is common and the goal of
therapy is normotensive blood pressure. This strategy does not
apply during pregnancy because the drugs may harm the foetus,
and placental perfusion (in theory) may be adversely affected by
antihypertensive drugs that diminish perfusion pressure.
Diuretics, although used to treat cardiac conditions during
pregnancy, are generally held to be contra-indicated in the
management of chronic hypertension during pregnancy
because pregnancy relies upon volume expansion to secure
an accelerated rate of delivery of oxygenated blood to the
peripheral tissues, including the placental bed. ACE inhibitors
are also contra-indicated because they may interfere with the
physiological regulation of uterine blood flow through local
uterine mechanisms. More seriously, they are associated with
neonatal renal failure in children of women treated with them
during pregnancy. Of the other categories of antihypertensive
drugs, beta-blockers are also relatively contra-indicated, being
considered to be an independent risk factor for the development
of intra-uterine growth restriction.
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Antihypertensive therapy during pregnancy in chronically
hypertensive women is usually secured through the use of alpha-
methyldopa or calcium channel blockers. The aim of treatment
is to reduce the occurrence of severe hypertension to safer levels
of blood pressure. Practically, the threshold for introducing
treatment is a sustained increase in blood pressure to above
160/110 mmHg to levels below this without seeking to reduce the
pressure to normotensive levels.
The complications of chronic hypertension during pregnancy
may extend to various forms of cardiac decompensation,
depending on the severity of the condition. Hence, hypertensive
cardiomyopathy is rarely seen in relatively young women with
chronic hypertension, although it may develop and can give rise
to maternal mortality.
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More commonly, diastolic dysfunction
caused by changes in left ventricular morphology may result
in the onset of increasing dyspnoea in the third trimester as
the volume expansion peaks out. Patients in this category are
otherwise well, without any signs of superimposed pre-eclampsia.
This is one circumstance where diuretic therapy may result in
rapid clinical improvement and resolution of symptoms that will
allow the pregnancy to continue to term.
Obstetric intervention is not commonly required in chronically
hypertensive women. However, some mild degree of foetal
growth restriction may be present and the risk of superimposed
pre-eclampsia cannot be excluded with absolute certainty.
Consequently, induction of labour is usually recommended
for women who do not labour spontaneously before 40 weeks’
gestation.
Latent hypertension
Pregnancy may render overt hypertension that is not yet clinically
manifest outside of pregnancy. Women who have a strong familial
history of hypertension, whose genetic predisposition will manifest
as essential hypertension in later life, may become hypertensive
during pregnancy. The mechanism is thought to be related to
subnormal pregnancy vasodilatation in vessels, with a hereditary
defect in vasoregulation. In this circumstance, the increased
intravascular volume of pregnancy cannot be accommodated by
adequate vasodilatation, with a rise in blood pressure developing
in the late second to third trimester of pregnancy.
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This condition should be managed according to the same
principles as those outlined for women with chronic hypertension.
The outcome of the pregnancy is usually unaffected and the
only consideration might be the need for induction of labour in
women not yet delivered by 40 weeks’ gestation.
Physiological hypertension
Hypertension does not always indicate disease. Pregnancy is
characterised by massive plasma volume expansion, and the
cardiovascular adaptation needed to accommodate this increased
intravascular volume is that of equally massive peripheral
vasodilatation. The net consequence of this is a fall in blood
pressure during the second trimester, with increasing levels
of blood pressure closer to term. The entire adaptation is
mediated by the placenta, and the adequacy of the pregnant
physiological change depends on the amount of biochemically
active trophoblast in the uterus. Hence women with multiple
pregnancies or those who have singleton pregnancies with a
large placenta will have a greater degree of volume expansion
than those with a smaller placental mass. The consequences of
this may be a supraphysiological increase in plasma volume that
exceeds the degree of compensatory vasodilatation close to term.
These individuals have normal pregnancies in every respect, with
normally grown babies and no other signs of pre-eclampsia. This
is not a condition requiring treatment or intervention and should
be recognised as a variant of normal.
3
The difficulty of managing these patients lies in being certain
that the distinction can be safely made between physiological
hypertension and pre-eclampsia. For this reason, many of these
women would be allowed to continue to term but induction of
labour would be justified at 40 weeks’ gestation
General evaluation of patients with hyperten-
sive disorder of pregnancy
Determining whether high blood pressure identified during
pregnancy is due to pre-eclampsia or chronic hypertension is
sometimes a challenge to the physician, especially if there are
no recorded blood pressures available from the first half of
the gestation. Clinical characteristics obtained through a good
history, physical examination and some laboratory investigations
may be used to help clarify the diagnosis.
Relevant history the physician must take
The time of detection of hypertension is very important.
Hypertension occurring before 20 weeks’ gestation is
almost always due to chronic hypertension, while new-onset
hypertension after 20 weeks’ gestation should lead to a suspicion
of gestational hypertension. Worsening hypertension after 20
weeks of gestation should lead to careful evaluation for the
manifestations of pre-eclampsia.