Introduction

Hypertension in pregnancy involves a significant risk to both mother and baby. Although the incidence of eclampsia is falling, hypertension in pregnancy still results in some maternal deaths, and can cause miscarriages, preterm deliveries, and small for date babies due to placental problems. Mothers can be left with chronic hypertension and increased lifelong cardiovascular risk.¹

• Chronic hypertension affects 1 to 5% of pregnancies.²
• Pregnancy-induced hypertension (now preferably known as gestational hypertension) affects 5 to 10% of all pregnancies. It is more common in first pregnancies (up to 25%).²

Hypertension in pregnancy includes:

• Gestational hypertension - pregnancy-induced hypertension which develops after 20 weeks' gestation and may be either transient hypertension of pregnancy or chronic hypertension identified in the latter half of pregnancy.
  • Pre-eclampsia: pregnancy-induced hypertension in association with proteinuria and/or oedema or both.
  • Eclampsia - occurrence of one or more convulsions superimposed on pre-eclampsia.
    
    See separate article 'Pre-eclampsia and eclampsia'.
• Pre-existing hypertension: is defined as a systolic blood pressure (BP) of 140 mm Hg or greater, and/or a diastolic BP of 90 mm Hg or more, either pre-pregnancy or at booking (before 20 weeks).
  • Pre-eclampsia in addition to pre-existing chronic hypertension.

Epidemiology

Management

Patients with pre-existing hypertension who become pregnant

• Review medication and inform the patient of the risks involved with some medications. Those on angiotensin-converting enzyme (ACE) inhibitors or angiotensin-II receptor antagonists (AIIRAs) should be switched from these as soon as possible, as there is an increased risk of congenital abnormalities if these drugs are taken during pregnancy. Ideally this will have been done at a pre-pregnancy counselling session, but if not it should be done as early as possible in the pregnancy. Chlorothiazide should also be avoided as this carries an increased risk of congenital abnormality and neonatal complications.³
• Aim to keep BP lower than 150/100 mm Hg (140/90 mm Hg if target organ damage) although do not seek to lower the diastolic below 80 mm Hg.
• Encourage women to keep their dietary sodium intake low, i.e. by reducing or substituting sodium salt.
• Test for proteinuria regularly - if this shows ≥1+ arrange a spot urinary protein:creatinine ratio or 24-hour urine collection to quantify proteinuria. There is significant proteinuria if urinary protein:creatinine ratio >30 mg/mmol or 24-hour urine collection >300 mg protein (treat patient as for pre-eclampsia - see 'Pre-eclampsia (hypertension with proteinuria and oedema)', below).
• Ultrasound examination is used to assess fetal growth and amniotic fluid volume (with umbilical artery Doppler velocimetry) at 28-30 weeks and 32-34 weeks.
• After delivery - If methyldopa is used - switch back to pre-pregnancy antihypertensive regime within 2 days of delivery.³

Gestational hypertension

• Assess severity:
  • Mild: 140-149/90-99 mm Hg. For patients presenting before 32 weeks (or at high risk of pre-eclampsia), measure BP twice a week; otherwise, measure BP no more often than weekly. Check urine for protein at each visit.
  • Moderate: 150-159/100-109 mm Hg. Monitor BP twice a week - start labetolol (alternatives are methyldopa or nifedipine) to keep systolic BP <150 mm Hg and diastolic BP between 80-100 mm Hg. Dip urine for protein at each visit. Arrange initial blood tests for FBC, electrolytes, renal function, and LFTs. Subsequent blood tests are not necessary if no proteinuria.
  • Severe: ≥160/110 mm Hg. Admit to hospital and treat as for moderate (above) to keep systolic BP <150 mm Hg and diastolic BP between 80-100 mm Hg. Measure BP at least 4 times a day and check urine for protein daily. Weekly blood tests for FBC, electrolytes, renal function, and LFTs. Check BP and urine twice weekly (and continue weekly blood tests) when discharged (once BP is in target range).
• Perform ultrasound examination at 34 weeks to assess fetal growth and amniotic fluid volume (with umbilical artery Doppler velocimetry) if mild or moderate gestational hypertension develops before this time. Arrange these tests and cardiotocography urgently whenever severe gestational hypertension is diagnosed.
• After birth measure BP daily for the first 2 days after birth, at least once between day 3 and day 5, then as clinically indicated. Continue on antihypertensive medication, but reduce or stop if BP is seen to be falling - particularly if it falls below 130/80 mm Hg. Switch women from methyldopa to an alternative within 2 days of delivery. Women with mild hypertension not requiring treatment during pregnancy should be started on antihypertensive medication postnatally if their BP is ≥150/100 mm Hg.

Pre-eclampsia (hypertension with proteinuria and oedema)

• Admit and monitor the patient in hospital. Always ask about headache and epigastric pain each time BP is taken to alert for any indication of progression towards eclampsia.
• Assess severity:
  • Mild: 140-149/90-99 mm Hg. Monitor BP at least 4 times per day. Twice weekly blood tests for FBC, electrolytes, renal function, and LFTs.
  • Moderate: 150-159/100-109 mm Hg or Severe: ≥160/110 mm Hg. Monitor BP at least 4 times per day. Start labetolol (or alternative) to keep systolic BP <150 mm Hg and diastolic BP between 80-100 mm Hg. Blood tests 3 times per week.
• Perform ultrasound examination to assess fetal growth and amniotic fluid volume (with umbilical artery Doppler velocimetry) and cardiotocography whenever pre-eclampsia is diagnosed.
• Repeat cardiotocography if there is a change in fetal movements, vaginal bleeding, abdominal pain or a deterioration in maternal condition. ³
• Pre-eclampsia will usually be managed conservatively (i.e. without delivery of the baby) until at least until 34 weeks. The management plan for delivery (including thresholds for early delivery) will be discussed with the parents on an individual basis and documented in the notes. Patients with mild or moderate pre-eclampsia are usually delivered between 34⁺⁰ to 36⁺⁶ weeks depending on assessment of risk and availability of a special care baby unit, with fetal monitoring and after a course of corticosteroids to reduce the risk of infant respiratory distress syndrome (if appropriate).
• Signs of complications developing include headache, epigastric pain, papilloedema, hepatic tenderness, signs of clonus (>3 beats), HELLP syndrome (= Haemolysis, EL (elevated liver) enzymes, LP (low platelet) count), platelet count falling (below 100 x 10⁹/L), abnormal liver enzymes (ALT or AST >70 IU/L). Consider anticonvulsants (usually intravenous magnesium sulphate).³
• Intrapartum - with mild and moderate hypertension (140/90-159/109 mm Hg), measure BP hourly; with more severe hypertension, measure continually.
• After birth, stop methyldopa (if used) within 2 days and avoid diuretics if breast-feeding, measuring BP at least 4 times daily whilst in hospital. Continue to ask about headaches and epigastric pain whenever BP is taken. Measure FBC, LFT and creatinine 72 hours after birth and only repeat after this if abnormal. Step down care (i.e. to community midwives) when BP <150/100 mm Hg and blood tests stable or improving without any pre-eclamptic symptoms.
• Reduce BP treatment if BP falls to <130/80 mm Hg (consider reducing when <140/90 mm Hg).
• Measure BP every 1-2 days for up to 2 weeks after transfer to community care (or until antihypertensive treatment stopped). Continue to monitor (i.e. weekly) and arrange medical review at two weeks postnatal if still requiring medication. Monitor BP at least until the 6-week check where a urine dip should also be performed (and arrange repeat FBC, creatinine and LFTs unless they have previously returned to normal).

Complications

• Pregnant women with chronic hypertension are at increased risk of pre-eclampsia, eclampsia and placental abruption.

Prognosis

• Hypertensive diseases of pregnancy remain the second leading cause of direct maternal deaths in the UK.
• Most women with pre-existing mild-to-moderate hypertension (BP less than 160/110 mm Hg) are at low risk of perinatal complications.
• The risk of complications (e.g. pre-eclampsia, placental abruption, impaired fetal growth and premature birth) are increased in severe hypertension.
• Gestational hypertension: similar risks to normotensive women, but 40% of those presenting before 34 weeks' gestation will go on to develop pre-eclampsia.
• Hypertension and/or proteinuria is the leading single identifiable risk factor in pregnancy associated with stillbirth.

Prevention

• Low-dose aspirin: see recommendation in high-risk groups as detailed under 'Epidemiology', above.
• Calcium supplementation: appears to reduce the risk of high BP in pregnancy, particularly for women at high risk of gestational hypertension and in communities with low dietary calcium intake.⁵

Document references

1. Hypertension in pregnancy, NICE Clinical Guideline (August 2010); The management of hypertensive disorders during pregnancy
2. Magee LA, Ornstein MP, von Dadelszen P; Fortnightly review: management of hypertension in pregnancy. BMJ. 1999 May 15;318(7194):1332-6.
3. Hypertension: management of hypertension in adults in primary care, NICE Clinical Guideline (August 2011)
4. Antenatal care: routine care for the healthy pregnant woman, NICE Clinical Guideline (March 2008)
5. Hofmeyr GJ, Atallah AN, Duley L; Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. 2006 Jul 19;3:CD001059. [abstract]

Internet and further reading

• Gibson P et al; Hypertension and Pregnancy, Medscape, Mar 2011