Complicated pregnancy clinic: hypertension

Hypertension specialist Dr Tarek Antonios outlines how to manage patients at risk from hypertensive complications in pregnancy

Hypertension – including in pregnancy – is diagnosed if clinic BP is persistently (measured several times over two to four weeks) above 140/90mmHg. The diagnosis should be confirmed by either 24-hour ambulatory BP monitoring or home monitoring. If readings are above 135/85mmHg, hypertension is confirmed. 

Hypertensive disorders of pregnancy (HDP) affect about 10% of pregnancies worldwide and are important causes of maternal, foetal and neonatal morbidity and mortality. HDP also increase the risk of future cardiovascular diseases not only in mothers but also in the offspring in later life. 

HDP incorporates any form of hypertension during pregnancy, defined by systolic BP of 140mmHg or higher or diastolic BP of 90mmHg or higher (see box 1). The hypertension may be mild (between 140/90mmHg and 159/99mmHg) or severe (160/100mmHg or above).

Chronic hypertension is defined as high BP that is present before pregnancy or diagnosed for the first time before the 20th week of gestation. 

Gestational hypertension, or pregnancy-induced hypertension, is new-onset hypertension diagnosed after 20 weeks’ gestation in the absence of proteinuria that resolves within three months after the birth. 

Pre-eclampsia or toxaemia of pregnancy is defined as new-onset hypertension after 20 weeks of pregnancy and the presence of either proteinuria (urine PCR of 30mg/mmol or higher, or ACR of 8mg/mmol or higher, or 2+ on dipstick testing) or maternal organ dysfunction (increased serum creatinine, high liver enzymes, persistent headache, visual disturbances, low platelet count, microangiopathic haemolytic anaemia) or uteroplacental dysfunction (foetal growth restriction, abnormal umbilical artery Doppler, or stillbirth). 

Risk factors for pre-eclampsia
There are several risk factors for pre-eclampsia including:

• Chronic hypertension
• Hypertensive disease in a previous pregnancy
• Chronic kidney disease
• Systemic lupus erythematosus
• Antiphospholipid syndrome
• Type 1 or type 2 diabetes;
• Nulliparity
• Age 40 years or over
• Interval between pregnancies of >10 years
• Obesity with BMI of ≥35 at first antenatal visit
• Family history of pre-eclampsia
• Multi-foetal pregnancy.

Women at risk of developing pre-eclampsia are advised to take 75–150mg of aspirin daily from 12 weeks gestation until the birth to help prevent pre-eclampsia. The protective effect of aspirin in pre-eclampsia is not understood.

Prenatal care for patients at risk of HDP
NICE recommends that women with pre-existing (chronic) hypertension who might become pregnant should be offered a referral to a hypertension specialist to discuss treatment. ACE inhibitors and ARBs should not be prescribed to hypertensive women who are at risk of getting pregnant, and should be stopped if women do get pregnant as these drugs increase the risk of congenital anomalies. Similarly, thiazide and thiazide-like diuretics are associated with an increased risk of congenital abnormalities and should be avoided if possible. Non-pharmacological management of HDP should follow the usual lifestyle advice for chronic hypertension.

Pharmacological treatment of HDP
The following drugs are recommended for the treatment of HDP if systolic BP is 140mmHg or higher or diastolic BP sustained at 90mmHg or higher: 

1. Labetalol.
2. Nifedipine (if labetalol is not tolerated).
3. Methyldopa (if both labetalol and nifedipine are not tolerated).

The aim of treatment is to reduce BP to 135/85mmHg or lower.

Exclusion of secondary causes of hypertension
In the majority of patients with hypertension no identifiable cause for their high BP can be found and so they are diagnosed with primary (essential) hypertension. However, in 10-20% of subjects a secondary and potentially curable cause can be found. Box 3 summarises the common causes of secondary hypertension. It is more likely for secondary hypertension to be diagnosed in patients under 40 years, those with severe or resistant hypertension, those with abnormal biochemistry (hypokalaemia, hypercalcaemia, metabolic alkalosis) or suggestive symptoms (excessive sweating, palpitations, panic syndrome-like symptoms). It is important to stress that undiagnosed secondary hypertension in pregnant women may pose a significant risk if not managed. 

For example, the most common cause of severe or resistant hypertension in young females is fibromuscular dysplasia (FMD) renal artery stenosis. FMD may be associated with renal artery aneurysms, which may rupture during pregnancy and cause catastrophic internal bleeding. Likewise, a pheochromocytoma, though very rare, carries a risk of mortality as high as 58% for both mother and foetus if untreated. Women with suspected secondary forms of hypertension should be referred to a hypertension specialist so they can be diagnosed and treated before conception.

Postnatal monitoring of BP
Women with HDP may require antihypertensive treatment in the postnatal period. NICE recommends that BP is measured daily for the first two days after birth, then at least once between days three and five, and as clinically indicated if antihypertensive treatment is changed after birth. The aim is to keep BP below 140/90mmHg. If methyldopa is used to treat chronic hypertension during pregnancy, it should be changed to another treatment by two days after birth. 

In my practice, I advise women with a history of HDP to invest in a home BP machine and to monitor on a regular basis. If their home BP becomes low or they feel dizzy on treatment they should be reviewed in primary care. Women who are not able to invest in a home BP machine should be reviewed in primary care every one to two months.

Lactation while on antihypertensive medications
Most antihypertensive medications have not been tested in pregnant or breastfeeding women and emerge in very low levels in breast milk, which are unlikely to have an important clinical effect. However it is recommended that women with pre-term infants are advised to monitor their babies for lethargy, pallor, cold peripheries or poor feeding and seek further help. 

NICE’s guideline advises to offer enalapril tablets to treat hypertension in the postnatal period, with monitoring of maternal renal function and potassium. Additional drugs such as nifedipine, amlodipine, labetalol or atenolol may be used, but not ARBs or diuretics. 

Women with chronic hypertension who don’t intend to breastfeed can be switched back immediately to their pre-pregnancy antihypertensive medications.

Long-term monitoring of women with history of HDP
As mentioned earlier, HDP increases the risk of hypertension and cardiovascular disease mortality not only in affected mothers but also in their offspring in later life. Most CVD guidelines consider HDP to be an independent risk factor for future CVD and recommend these women have annual follow-up. It is estimated that the overall risk of HDP in future pregnancies is one in five. Women with a history of HDP need to modify their lifestyle to reduce their future CVD risk.

Key points

• Hypertensive disorders of pregnancy (HDP) affect about 10% of pregnancies worldwide and are important causes of maternal, foetal and neonatal morbidity and mortality
• The term HDP incorporates all forms of hypertension that occur in pregnancy – pre-existing (chronic) hypertension as well as gestational hypertension and pre-eclampsia
• HDP increases the risk of future cardiovascular diseases not only in affected mothers but also in their offspring
• Individuals with pre-existing (chronic) hypertension should be referred to a specialist for counselling about the benefits and risks of treatment
• Individuals should stop treatment with ACE inhibitors or ARBs within 2 days of notification of pregnancy and be offered alternative treatments; those taking thiazide or thiazide-like diuretics should be advised of the risks and offered alternative treatments
• HDP should be treated with (in order of preference) labetalol, nifedipine or methyldopa. Target BP is below 135/85mmHg

Dr Tarek Antonios is a senior lecturer and consultant physician in cardiovascular and general medicine and is head of the blood pressure unit at St George’s University Hospital NHS Trust, London

Further reading

1.  NICE. NG 133. Hypertension in pregnancy: diagnosis and management. Link
2. Webster K, Fishburn S, Maresh M et al. Diagnosis and management of hypertension in pregnancy: summary of updated NICE guidance. BMJ 2019;366:l5119. Link