Hypertension is a common medical condition affecting many people worldwide, and it can pose a serious risk to both the mother and the developing fetus during pregnancy. Hypertension is the most common medical problem in pregnancy, complicating approximately 10-15% of pregnancies, and is the second leading cause of direct maternal deaths in the UK.
The exact causes of hypertension in pregnancy are not fully understood. However, several factors can contribute to the development of hypertension during pregnancy, including maternal age, obesity, pre-existing medical conditions (such as diabetes and kidney disease), and multiple pregnancies.
Women with hypertension during pregnancy have a higher risk of complications, including:
- Placental abruption
- Stroke
- Disseminated intravascular coagulation (DIC)
In the presence of maternal hypertension, the fetus has an increased risk of complications, including:
- Intrauterine growth restriction
- Prematurity
- Intrauterine death
The management of hypertension in pregnancy depends on the type and severity of the condition. In general, treatment aims to lower blood pressure and prevent complications for both the mother and baby.
Types of hypertensive disorders seen in pregnancy
Four main types of hypertensive disorder are encountered in pregnancy:
Pre-existing or chronic hypertension:
This is defined as hypertension (systolic blood pressure of 140 mmHg or greater, and/or diastolic blood pressure of 90 mmHg or greater), either pre-pregnancy or at booking (before 20 weeks of gestation).
Gestational hypertension:
This is defined pregnancy-induced hypertension that develops after 20 weeks of gestation in women who did not have hypertension before pregnancy.
Pre-eclampsia:
This is defined as pregnancy-induced hypertension associated with proteinuria (0.3 g in 24 hours) and/or maternal organ dysfunction.
Eclampsia:
This is defined as the occurrence of one or more convulsions superimposed on pre-eclampsia.
Screening for hypertensive disorders in pregnancy
All pregnant women should have their blood pressure measured and their urine dipsticked for protein at every antenatal appointment.
In addition, all pregnant women should be counselled about the symptoms of pre-eclampsia (see below) and advised to seek an immediate medical review if they experience any of the following:
- Severe headache
- Visual problems (blurred vision, flashing lights)
- Severe subcostal pain
- Vomiting
- Sudden swelling of the face, hands or feet.
Pre-existing or chronic hypertension
For women with chronic hypertension, close blood pressure monitoring is recommended throughout pregnancy, and antihypertensive medication may be required to control blood pressure. Lifestyle advice should be given to the mother, including work, rest, exercise, a healthy diet, and restriction of dietary salt and weight. Specialist advice is often required due to the complexity of the situation.
Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) are associated with an increased risk of adverse fetal outcomes and congenital abnormalities if taken in pregnancy, particularly during the second and third trimesters. Thiazide and thiazide-like diuretics can reduce the blood flow in the placenta, and some studies have also shown that these diuretics can be associated with neonatal thrombocytopaenia. In most circumstances, these should be stopped and specialist advice and/or treatment with an alternative drug commenced if indicated.
If the mother is taking any other antihypertensive, continuation of treatment should be considered. It should be noted, however, that some women with chronic hypertension can have blood pressure within the normal range due to the physiological drop in blood pressure that occurs in early pregnancy, and continued treatment is not always necessary.
The current NICE guidelines recommend that an alternative antihypertensive treatment is required during pregnancy:
- First-line treatment is usually labetalol if not contraindicated.
- Consider nifedipine for women for whom labetalol is not suitable.
- Consider methyldopa if both labetalol and nifedipine are not suitable.
The target blood pressure following antihypertensive treatment in pregnancy is 135/85 mmHg.
Aspirin 75-150 mg can reduce the risk of pre-eclampsia and should be prescribed from 12 weeks gestation until birth.
At every antenatal visit:
- Blood pressure should be measured
- The urine should be dipsticked for protein
- The mother should be assessed for symptoms of pre- eclampsia
Gestational hypertension
Similarly to women with chronic hypertension, women with gestational hypertension require close blood pressure monitoring and fetal well-being. Antihypertensive medication is often unnecessary unless blood pressure remains consistently high or there are signs of pre-eclampsia. All women with new-onset hypertension should be assessed in secondary care by a specialist trained in managing hypertensive disorders of pregnancy. Management depends upon the severity of the hypertension.
Mild gestational hypertension (BP 140-149/90-99 mmHg):
- Careful monitoring is the mainstay of treatment
- Blood pressure should be measured twice a week
- The urine should be dipsticked for protein at every antenatal visit.
Moderate gestational hypertension (BP 150-159/100-109 mmHg):
- Antihypertensive medication should be commenced
- The first-line choice antihypertensive is labetalol (alternatives are methyldopa or nifedipine)
- The goal is to keep systolic BP <150 mmHg and diastolic BP between 80-100 mm Hg.
- Blood pressure should be measured twice a week
- The urine should be dipsticked for protein at every antenatal visit
- Arrange initial blood tests for FBC, electrolytes, renal function and LFTs.
Severe gestational hypertension (BP ≥160/110 mm Hg)
- Women with severe gestational hypertension should be admitted to hospital and monitored carefully
- The treatment is the same as that for moderate gestational hypertension
- Blood pressure should be measured at least four times daily, and urine dipsticked for protein daily
- Weekly blood tests should be arranged for FBC, electrolytes, renal function and LFTs.
Pre-eclampsia
Pre-eclampsia is relatively common and can become a life-threatening condition for both the mother and the fetus. The current NICE guidelines define pre-eclampsia as the new onset of hypertension after 20 weeks of pregnancy and the coexistence of 1 or more of the following new-onset conditions:
- Proteinuria, or
- Maternal organ dysfunction:
- Renal insufficiency
- Liver involvement
- Neurological
- Haematological complications
- Uteroplacental dysfunction
Pre-eclampsia is a relatively common condition but may become life-threatening for the mother and the fetus.
The risk factors for pre-eclampsia are summarised in the following table:
| High-risk factors | Moderate-risk factors |
|---|---|
| History of hypertensive disease in a previous pregnancy Chronic hypertension Chronic kidney disease Autoimmune disease (e.g. SLE, antiphospholipid syndrome) Type 1 or 2 diabetes mellitus | Aged 40 or older First pregnancy Multiple pregnancy Pregnancy interval of >10 years BMI >35 kg/m2 Family history of pre-eclampsia |
Women are considered to be at high risk of pre-eclampsia if they have one or more high-risk factors or two or more moderate-risk factors. Women at high risk should have consultant-led antenatal care, take 75-150 mg aspirin daily from 12 weeks gestation until birth and be counselled about healthy lifestyle advice.
Severe pre-eclampsia is defined as diastolic blood pressure (BP) of at least 110 mmHg or systolic BP of at least 160 mmHg, and/or symptoms, and/or biochemical and/or haematological impairment. In severe pre-eclampsia, the fetus and/or newborn may have hypoxia-induced neurological damage. Prompt recognition and urgent referral to secondary care are imperative. The following are features of severe pre-eclampsia:
- Severe proteinuria
- Oliguria (urine output < 500 ml/24 hours)
- Neurological symptoms and signs, e.g. headache, papilloedema, clonus
- Platelet count <100 x 109/L
- Epigastric pain and/or right upper quadrant tenderness
- Elevated liver enzymes (AST and ALT)
Antihypertensive treatment should be commenced in women with a systolic BP over 160 mmHg and/or a diastolic BP over 110 mm Hg. In women with other markers of potentially severe disease, treatment can be considered for lower degrees of hypertension. The first line treatment choice is labetalol, nifedipine is used second line, and methyldopa can be used if neither labetalol nor nifedipine is suitable.
The only cure for pre-eclampsia is the delivery of the fetus and placenta. However, premature delivery can adversely affect the baby’s health due to underdevelopment and low birth weight. Hence, a customised management plan for delivery, including when to consider early delivery, should be jointly discussed by the consultant and the woman.
Eclampsia
Eclampsia is defined as the occurrence of one or more convulsions superimposed on pre-eclampsia. It is considered a medical emergency and requires immediate treatment to prevent harm to both the mother and the baby. Eclampsia can lead to complications such as stroke, organ damage, placental abruption, and fetal distress.
The mother should be placed in the left lateral position and be resuscitated using an ABC approach.
Magnesium sulphate is the therapy of choice to control seizures in eclampsia. The Collaborative Eclampsia Trial regimen for administration of magnesium sulphate should be used:
- A loading dose of 4 g should be given intravenously over 5 to 15 minutes
- This should be followed by an infusion of 1 g/hour maintained for 24 hours.
- If the woman has had an eclamptic seizure, the infusion should be continued for 24 hours after the last seizure
- Recurrent seizures should be treated with a further dose of 2-4 g given intravenously over 5 to 15 minutes
Reducing severe hypertension is essential to reduce the risk of cerebrovascular accident and may also reduce the risk of further seizures. Intravenous labetalol and hydralazine are the two most commonly used drugs.
Delivery of the fetus and placenta is the only cure for eclampsia, and following stabilisation, the patient should be prepared for an emergency caesarean section.
Reference:
NICE guideline on Hypertension in pregnancy: diagnosis and management
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