Pre-existing high blood pressure in pregnancy

Pre-existing high blood pressure (hypertension) in pregnancy is when you're diagnosed with hypertension before you become pregnant, or before you are 20 weeks pregnant.

Hypertension is when the pressure in your blood vessels (arteries) is too high. Hypertension is diagnosed when your blood pressure measures 140/90 mmHg (millimetres of mercury) or higher, on 2 or more occasions at least 4 hours apart. Read more about hypertension.

Pre-existing hypertension in pregnancy, sometimes called chronic hypertension, can make you more likely to develop pre-eclampsia (see the complications section below) or have complications during your pregnancy. Therefore, your blood pressure must be closely monitored and may have to be treated with blood pressure lowering medicines (antihypertensives). 

High blood pressure often runs in families. Kidney or endocrine (hormonal) disease, sleep apnoea and diabetes can affect blood pressure. Eating too much salt, drinking too much alcohol, high stress levels, being overweight and not moving around enough each day can also contribute to high blood pressure and heart disease. 

The effects of high blood pressure on your blood vessels are made worse by:

• cigarette smoking
• high levels of saturated fat in your diet
• high levels of cholesterol in your blood.

Some medicines may cause raised blood pressure or make controlling it more difficult. These medicines include:

• the combined contraceptive pill
• non-steroidal anti-inflammatories (NSAIDs)
• some nasal drops and sprays
• some cough medicines, eye drops and appetite suppressants.

The main complication of having pre-existing hypertension in pregnancy is developing pre-eclampsia. Your chance of developing pre-eclampsia increases by 20% if you have pre-existing hypertension. This is why you must have your blood pressure monitored closely during pregnancy if you have pre-existing hypertension.

Other complications include:

• stroke
• heart failure
• kidney failure
• premature delivery of your baby (before 37 weeks)
• poor growth of your baby
• placental abruption (severe bleeding from your placenta).

If you have pre-existing hypertension, you will usually be diagnosed before pregnancy or you may be diagnosed at your first antenatal visit. You may also already be on antihypertensive medications.

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At each antenatal visit, your midwife or lead maternity carer (LMC) will check your blood pressure and test your urine for protein. They will also check for any of the following symptoms:

• severe headache
• changes in eyesight such as seeing spots, flashing lights or floaters, blurry vision
• pain in your upper belly, tummy area or shoulder
• sudden and new swelling in your face, hands or eyes (some feet and ankle swelling is normal during pregnancy)
• passing only small amounts of urine
• sudden weight gain (more than 1 kg in a week or more than 3 kg in a month)
• nausea or vomiting later in your pregnancy (not the morning sickness of early pregnancy)
• difficulty breathing or feeling short of breath.

These symptoms are warning signs of pre-eclampsia. A sudden increase in blood pressure is often the first sign of a problem.

If you have pre-existing hypertension you'll need to be closely monitored throughout the pregnancy. You will be taught the signs and symptoms of pre-eclampsia to watch out for as it's important to contact your midwife or healthcare provider if you develop any of these symptoms.

Treatment depends on how high your blood pressure is and whether you have developed pre-eclampsia.

Planning a pregnancy?

If you're taking medicines to treat high blood pressure before pregnancy and you're planning a pregnancy, speak to your healthcare provider or midwife about reviewing your medication before you become pregnant. Your medication will be changed to one that is considered safe in pregnancy. 

Found out you're pregnant?

If you're taking medicines to treat high blood pressure and you have just found out that you are pregnant, contact your healthcare provider immediately so that your medication can be reviewed. 

Commonly prescribed antihypertensives in pregnancy

Commonly used blood pressure medicines (antihypertensives) during pregnancy include:

• labetalol
• nifedipine
• methyldopa.

When deciding whether or not to take antihypertensive medicines during pregnancy, your healthcare provider will discuss the importance of the medicine and the possible risks to you or your baby – some of which will depend on how many weeks pregnant you are.

Additional medicines

If you have pre-existing hypertension you have a higher chance of developing pre-eclampsia and other complications during pregnancy, so you may also be given medicines to help prevent pre-eclampsia, such as: 

• aspirin 100 milligrams orally once daily
• calcium
• usual pregnancy vitamins including folic acid and iodine – these may be individual tablets or as part of a multivitamin such as Elevit®.

Antihypertensive medications that are not safe during pregnancy

Some medicines used to treat high blood pressure shouldn't be taken during pregnancy as they may harm a developing baby.

Examples of blood pressure medicines that should not be taken during pregnancy are:

• angiotensin-converting enzyme (ACE) inhibitors
  • Examples include captopril, cilazapril, enalapril, lisinopril, perindopril, quinapril
• angiotensin receptor blockers (ARBs)
  • Examples include candesartan, irbesartan, losartan
• diuretics (water pills)
  • Examples include bendroflumethiazide, chlortalidone, indapamide, furosemide, hydrochlorothiazide, amiloride. 

Severe hypertension or if pre-eclampsia develops

If your blood pressure becomes severely high, or you develop pre-eclampsia, you may be referred to an obstetrician or a specialist for treatment or monitoring. You may need to be admitted to hospital. You will need much closer supervision and will probably need to have your baby early.

The treatment and monitoring aim to keep you and your baby safe while your baby grows and develops as much as possible. If your baby does have to be delivered early there are treatments available to decrease the complications of being born prematurely.

Read more about pre-eclampsia.