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West Wiltshire Primary Care Trust
Maternity Services
GUIDELINES FOR THE MANAGEMENT OF ANTENATAL
AND POSTNATAL MILD TO MODERATE HYPERTENSION
Best practice points
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Severe hypertension must be identified and controlled to avoid the serious
complications of maternal vascular damage.
Mild to moderate hypertension alone is a significant risk factor for both preeclampsia and eclampsia.
The pharmacological treatment of hypertension, whilst reducing the risk of
developing severe hypertension, has not been shown to reduce the risks of
developing either pre-eclampsia or eclampsia. There is no evidence at present that
anti-hypertensives used for mild to moderate hypertension improve maternal or
neonatal outcome.
Background
Hypertension is the most common medical problem encountered in pregnancy and is
responsible for up to 25% of all antenatal admissions. Approximately 10% to 15% of
pregnant women have blood pressure measurements above the normal range. These
women fall into three main groups: Chronic hypertension, pregnancy-induced hypertension
or hypertension associated with pre-eclampsia. The latter represents a multi-system
disorder peculiar to pregnancy, which, whilst related to the other hypertensive disorders has
its own pathological process which has yet to be fully understood. It is important to
distinguish pre-eclampsia as a separate condition as it has a higher maternal and neonatal
morbidity and mortality rates. The incidence of severe pre-eclampsia is about 1%.
Eclampsia is rare (incidence 0.05%) but has a mortality of approximately 2% in the UK.
However, it is important to note that approximately one third of women fit for the first
time following normal or mild increases in blood pressure measurements.
Definitions
Hypertension
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Two readings of greater than, or equal to, 140/90 taken at least 4 hours apart.
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Or a single reading of greater than, or equal to, 170/110.
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Or an incremental rise in the diastolic BP, of 25mmHg above the booking blood
pressure.
Hypertension new to pregnancy manifesting after
20 weeks of gestation that is associated with a new
onset of proteinuria, which resolves after delivery.
Pre-eclampsia
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Pregnancy - induced hypertension
Hypertension new to pregnancy that resolves
after delivery but is not associated with
proteinuria.
Chronic hypertension
Hypertension that predates a pregnancy, appears
prior to 20 weeks of gestation or (in retrospect)
does not resolve after delivery.
Measuring blood pressure
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Blood pressure taken in the late second or third trimester should be taken with a
woman sitting or in a semi-reclining position. The arm to be used should be at the
level of the heart.
The appropriate size cuff should be used, at least 33 x 15 cm. A larger cuff for
women with an arm circumference of greater than 33 cm. A thigh cuff for women
with an arm circumference of greater than 41 cm.
Phase V (disappearance) rather than phase IV (muffling) of Korotkoff sounds should
be taken as the diastolic reading.
Note that automated devises can under-read blood pressure by significant amounts
in women with pre-eclampsia.
Treatment
This guideline deals with mild to moderate hypertension. It does not deal with severe
hypertension, pre-eclampsia or eclampsia (see guideline 210 – Protocol for the
management of severe eclampsia). However it is imperative that all members of the
team are familiar with the management of each of these conditions. Once the mean
arterial blood pressure (MAP) reaches 150, there is a loss of cerebral
autoregulation and the mother is at risk of cerebral haemorrhage. Blood pressures
of this magnitude are also associated with placental abruption, whatever the underlying
cause.
Mild to moderate hypertension in itself carries little risk to mother or fetus but is
important, as it alerts us to the development of the aforementioned conditions.
Antihypertensive treatment has not been shown to limit the progression to preeclampsia or eclampsia. However, antihypertensives have been demonstrated to
significantly reduce the risk of severe hypertension. This may in turn reduce the
number of admissions, inductions, emergency deliveries and iatrogenic neonatal
prematurity, although we await reliable evidence for an improvement in these
outcomes.
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Anti-hypertensives
First line therapies
Methyldopa
Methyldopa has been used for many years without any reports
of serious adverse effects. Follow-up studies have been done
on children up until the age of 7.
It does carry a risk of side effects for the mother which include
depression, sedation and postural hypotension and thus should
not be used in the postnatal period.
Dosage:
Labetolol
A loading dose of 500 mg should be given,
followed by a starting dose of 250 mg bd up to a
maximum dose of 1 g tds.
Labetolol has a better side effect profile than Methyldopa but
has less established follow-up data. Labetolol can be used as a
first line therapy in the third trimester but should be reserved as
a third line therapy earlier on in pregnancy as there are some
(yet unproven) concerns that b-blockers may inhibit fetal
growth. Labetolol is contraindicated in women with asthma.
Dosage:
A starting dose of 100 mg bd increasing to a
maximum dose of 500 mg tds.
Second line therapies
Nifedipine
Nifedipine is a calcium antagonist. It can be used together with
Methyldopa or as a single agent in women who do not tolerate
the first line therapies. Side effects include headache, facial
flushing and oedema.
Dosage:
Hydralazine
Starting dose 10 mg slow release bd
Maximum dose 40 mg slow release bd
Hydralazine acts as a vasodilator and has a similar side effect
profile to nifedipine. It can also be used either in conjunction
with or as an alternative to Methyldopa.
Dosage:
Starting dose 25 mg tds
Maximum dose 75 mg qds
Other antihypertensives
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Alpha blockers such as doxazocin may be used as third line therapy but doxazocin
accumulates in breast milk so prazocin should be used postnatally
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Diuretics should only be used in pregnancy for patients with heart failure and
pulmonary oedema. In all cases, they should be used in caution, with senior obstetric
and anaesthetic involvement.
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ACE inhibitors should not be used in pregnancy as they may cause renal failure
(leading to oligohydramnios) and hypotension in the fetus. Any woman already
taking an ACE inhibitor should be switched to Methyldopa in early pregnancy.
Use of ACE inhibitors in the first trimester is not associated with any structural
malformations so pre-conceptual cessation is not necessary.
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Postnatal treatment
Blood pressure rises after normal pregnancy, reaching a peak at about day 3 or 4.
Methyldopa should be stopped postpartum as, although it is safe to breast-feed, drugs
with fewer side effects can be used.
B-blockers including atenolol (50-100 mg once daily) and oxyprenolol (40-160 mg
bd) can be used in women who are not asthmatic. Either slow release (10-20 mg bd) or
long acting (60 mg once daily) nifedipine can also be used either alone or in
conjunction with a b-blocker. An ACE inhibitor (enalapril 5-10 mg once daily) may
also be an acceptable alternative. All the above are safe to use whilst breast feeding.
It is reasonable to discharge women postnatally provided their blood pressure has been
consistently recorded for the preceding 24 hours with systolic measurements below 160
and diastolic measurements below 100. Women with measurements equal to or above
these figures should have a further medical review, if still an inpatient; and should be
referred back into hospital for assessment, if in the community.
Women discharged on antihypertensives should be seen either by their GP or an
obstetrician at a six week follow-up appointment to rationalise their treatment. Few
women started on antihypertensives during pregnancy require continued
antihypertensive treatment beyond six weeks. However, women who develop
hypertension in pregnancy are at risk of developing hypertension later in life.
References
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Abalos E, Duley L, Steyn DW, Henderson-Smart DJ. Antihypertensive drug therapy for
mild to moderate hypertension during pregnancy.
The Cochrane Database of Systematic Reviews 2001, Issue 1. Art. No.: CD002252.
DOI: 10.1002/14651858.CD002252.
Magee LA, Duley L. Oral beta-blockers for mild to moderate hypertension during
pregnancy.
The Cochrane Database of Systematic Reviews 2003, Issue 3. Art. No.: CD002863.
DOI: 10.1002/14651858.CD002863.
NICE Guidelines Antenatal Care – Routine Care for the Healthy Pregnant Woman –
Clinical Guideline
National Collaborating Centre for Women’s and Children’s Health
Handbook of Obstetric Medicine (2nd edition) C Nelson-Piercy Dunitz, 1-84184-118-8
332 pages 2001
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